CN109270552B - Helicopter-mounted laser radar laser scanning attitude angle stabilizing method and device - Google Patents

Abstract

A method and a device for stabilizing a laser scanning attitude angle of a helicopter-mounted laser radar are disclosed, wherein a push-turn structure is adopted for the rotation of a laser reflector, so that the size of the laser reflector can be effectively increased, and the volume and the mass of the device can be reduced. The laser reflector is arranged on the magnetic universal ball bearing and swings and scans by taking the center of the ball as a rotation center, and laser pulses are reflected at the rotation center of the laser reflector. When the attitude angle of the airborne platform changes, two screw rod stepping motors are adopted to control the laser mirror to rotate reversely around the x axis and the y axis by a rolling angle and a half of a pitch angle in a linear pushing mode for compensation; and a z-axis stepping motor is adopted to drive the laser reflector to reversely rotate around the z-axis for compensating the yaw angle amplitude, so that the spatial direction of the laser scanning center is not influenced by the change of the attitude angle of the platform. The laser gyroscope is installed on the airborne platform, the MEMS gyroscope is installed on the laser reflector, and the normal of the laser reflector is controlled to point to the expected space direction by comparing the attitude angle measured values of the laser reflector and the MEMS gyroscope, so that the dynamic target is tracked and scanned in real time.

Description

Method and device for stabilizing attitude angle of laser scanning laser radar on helicopter

technical field

The invention relates to high-precision laser scanning technology of helicopter-borne laser radar, how to eliminate the influence of low-frequency fluctuation and high-frequency vibration of the attitude angle of the airborne platform on the laser point cloud, and proposes a method and device that can keep the attitude angle stable during laser scanning .

Background technique

Airborne laser radar (LiDAR), as a ground surveying and mapping device, can quickly and accurately collect large-scale laser point clouds of the measured terrain, and generate a digital surface model (DSM) of the measured terrain. As the basis for digitally describing terrain information, the digital surface model's accuracy has an important impact on subsequent scientific research and applications. Therefore, how to effectively improve the DSM accuracy generated by airborne LiDAR point cloud data has important practical significance.

Helicopters have been widely used as the payload platform of lidar. The helicopter is flexible in flight, can hover in the air, has a maximum speed of 300km/h, and has a flight altitude ranging from a few meters above the ground to 6000m in the air. models. Helicopters have some high-speed rotating parts such as rotors and tail rotors. These parts will vibrate violently when they work, resulting in high vibration and noise when the helicopter is flying. These shortcomings make the flight trajectory of the helicopter more complicated than that of the fixed-wing aircraft, and the attitude angle disturbance of the airborne platform is more obvious and complicated, including both low-frequency fluctuations and high-frequency vibrations, so it is difficult for the helicopter installed on the airborne platform LiDAR work can have serious repercussions. The complex attitude angle disturbance will change the exit space angle of the laser pulse beam emitted by the airborne LiDAR, resulting in extremely uneven distribution of the measured terrain laser point cloud. The accuracy of the DSM generated at the lower density of the laser point cloud deteriorates, and the detailed information of the measured terrain in this area cannot be clearly described. Therefore, in order to effectively improve the accuracy of DSM, it is necessary to effectively solve the adverse effects of complex changes in the attitude angle of the helicopter load platform on laser scanning.

In order to solve this problem, the common method at home and abroad is to make a stable platform to achieve the purpose of isolating the load and the load platform. In recent years, there have been a lot of research literature on stable platforms, and the technology of stable platforms has been quite mature, but most of the research is limited to the general stable platform that maintains the overall attitude angle stability of the equipment. The universal stable platform is mainly used to eliminate the influence of carrier attitude angle vibration on equipment and instruments that require precise positioning, and can adapt to various carriers, such as automobiles, airplanes, ships, etc. For the airborne LiDAR with higher real-time requirements, the compensation effect of the general stabilized platform is poor due to its large residual attitude angle error. The goal of attitude angle compensation for airborne LiDAR is to quickly correct the outgoing spatial direction of the laser pulse beam rather than the spatial orientation of the entire device. Therefore, it is difficult for a general-purpose stable platform to achieve a satisfactory attitude angle compensation effect for airborne LiDAR. .

At present, a certain degree of research has been carried out on airborne LiDAR attitude angle compensation at home and abroad. For example, Gat proposed a general attitude angle optics for push-broom cameras and laser scanners on airborne or spaceborne platforms. device; Xu Lijun, Wang Jianjun, etc. in patents ZL201010183492.4 and ZL201010180527.9 respectively proposed a method and device for real-time compensation of airborne lidar pitch angle deviation and a real-time compensation for airborne lidar roll angle deviation Method and device, but only limited to the stable compensation of a single attitude angle. Some of the world's mainstream LiDAR manufacturers have also begun to pay attention to the research of attitude angle optical compensation devices suitable for airborne LiDAR systems. For example, two products of Leica and Optech have added a roll angle compensation method. In summary, the laser scanning attitude angle stabilization method for airborne LiDAR will become an important research direction for LiDAR products.

Contents of the invention

In order to avoid the influence of complex changes in the attitude angle of the airborne platform during the laser scanning of the helicopter-borne LiDAR, the present invention proposes a method and device for stabilizing the laser scanning attitude angle of the helicopter-borne LiDAR. During the design, the following factors were mainly considered: (1) Due to the long measurement distance of the airborne laser radar, the area of the laser scanning mirror should be designed to be large enough to effectively collect laser echo signals; (2) The helicopter load platform The change of the attitude angle is complex, including the low-frequency and large-scale attitude angle fluctuations caused by gusts and turbulence, and the high-frequency attitude angle vibration of the engine and the rotating mechanism of the helicopter. Therefore, the compensation control of the attitude angle by laser scanning is required to have a large bandwidth , to achieve fast control response and compensate for high-frequency attitude angle vibrations. (3) The stabilization and compensation of three attitude angles can be realized simultaneously. (4) Since it is installed as airborne equipment, the stabilizer should be small in size and light in weight. Therefore, after analysis and comparison, the designed helicopter-mounted lidar laser scanning attitude angle stabilization device is different from the general-purpose three-axis rotation stabilized platform, but adopts a push-and-turn structure, which can simultaneously realize real-time compensation of the complex vibration of the three-axis attitude angle. The scanning mirror is large, and the device has the advantages of small size and light weight. A MEMS gyroscope is installed on the scanning mirror to obtain real-time measurements of the three attitude angles of the scanning mirror relative to the local reference coordinate system. Therefore, the laser scanning direction of the scanning mirror can be pointed to the desired direction by controlling the spatial orientation of the normal line of the scanning mirror. the spatial orientation. In addition, when the attitude angle of the helicopter load platform changes, two screw stepping motors are used to control the scanning mirror to rotate in the opposite direction around the x-axis (roll angle rotation axis) and y-axis (pitch angle rotation axis) in the form of linear push. Angle to compensate the roll angle and pitch angle disturbance; use the z-axis stepping motor to drive the scanning mirror to rotate a certain angle around the z-axis to compensate the yaw angle disturbance, so that the laser scanning and emission direction will not be affected by the change of the attitude angle of the airborne platform , always expects to point to. This attitude angle stabilization method is also very suitable for laser tracking and scanning of dynamic targets. Although the attitude angle of the aircraft load platform is constantly changing, the spatial orientation of the laser scanning center can always remain unchanged, or it can be controlled in real time. spatial orientation.

The invention proposes a method and device for stabilizing the attitude angle of a laser scanning laser radar carried by a helicopter. 2), laser pulse transmitter (3), MEMS gyroscope (4), airborne platform (5). The laser scanning attitude angle stabilizing device (1) includes a mechanical transmission part and an attitude angle stabilizing device controller. The reference coordinate system is XYZ-O, where the X direction is the forward direction of the aircraft, Z is the vertical downward direction, and Y is the right direction of the aircraft. The coordinate origin O is the laser scanning optical center, that is, the rotation center of the laser mirror (101), that is, the laser pulse reflection point of the laser mirror (101). The laser pulse emitter (3) is consolidated with the airborne platform (5), and the laser emission direction points to the center of the laser reflector (101) and shoots to the measured ground. The laser gyroscope (2) is used to measure the attitude angle change of the airborne platform (5) in real time, and the laser reflector (101) is controlled to rotate accordingly, so as to stabilize the spatial direction of the laser scanning output. In addition, the MEMS gyroscope (4) is installed on the back of the laser reflector (101) for measuring the actual three-dimensional attitude angle of the laser reflector (101).

Wherein, by comparing the measured values of the laser gyroscope (2) and the MEMS gyroscope (4), the angle difference between the two is obtained, and the center normal of the laser reflector (101) can be controlled to point to any desired spatial orientation , Laser tracking scanning and detection of dynamic and static targets. On the other hand, when the airborne platform (5) has a three-dimensional attitude angle change, control the x-axis and y-axis of the laser mirror (101) to reversely rotate the roll angle and pitch angle of the airborne platform (5) respectively. half of the value, and the z-axis reversely rotates with the same amplitude as the yaw angle measurement value of the airborne platform (5), so that the spatial orientation of the laser beam emitted after being reflected by the laser reflector (101) is not random. The influence of the three-dimensional attitude angle change of the carrying platform (5). At the same time, the laser reflector (101) also needs to realize the laser scanning function. Therefore, the control movement of the laser mirror (101) is the superposition of three control signals, one is the scanning and swinging movement around the x-axis to realize the laser two-dimensional scanning; the other is the real-time change of the three-dimensional attitude angle of the airborne platform (5). compensation movement; the third is that the laser reflector (101) normal points to realize the real-time tracking movement of the space dynamic target.

Among them, the mechanical transmission part of the laser scanning attitude angle stabilization device (1) includes: laser reflector (101), cross-shaped mirror support rod (102), ball joint universal bearing (103), motor bracket (104), slotting Stainless steel small hemisphere (105), magnetic steel concave sphere (106), center column (107), x-axis screw stepping motor (108), y-axis screw stepping motor (109), axial deflection hinge ( 110), miniature ball bearings (111), z-axis stepper motor (112), support column (113), mounting base (114), center column chassis (115), longitudinal deflection hinge (116), counterweight (117 ), straight slider (118), anti-backlash lead screw nut (119). The laser reflector (101) can realize three-axis rotation, and the coordinate origin O of the reference coordinate system XYZ-O is the symmetry center of the laser reflector (101), that is, the rotation center of the laser reflector and the laser pulse reflection point. The mirror symmetry center of the laser reflector (101) coincides with the rotation center of the laser reflector (101), and its spatial position is fixed by a central column (107). The x-axis and y-axis in the two directions of the two mutually perpendicular sides of the laser reflector (101) are respectively the rotation axes of the roll angle (x-axis) and the pitch angle (y-axis) of the airborne platform, which can be stepped by the x-axis screw The motor (108) and the y-axis screw stepper motor (109) respectively drive the laser mirror (101) to rotate around the y-axis and the x-axis. The center column (107) can rotate around the z-axis, which is the same as the rotation axis of the yaw angle. The z-axis stepping motor (112) fixed on the installation base (114) drives the center column (107) to rotate, thereby driving The laser reflector (101) rotates around the z axis.

Wherein, the center of the mirror surface and the midpoints of the four sides of the mirror surface of the laser reflector (101) are control points constraining the rotation orientation of the mirror surface in space. The four linear slides (118) are connected by ball joint bearings (103). Rolling bearings are installed at the two ends of the four straight-moving slide blocks (118), which can move up and down along the track grooves of the four motor supports (104) respectively. The X-axis lead screw stepper motor (108) and the Y-axis lead screw stepper motor (109) are respectively installed in the two motor brackets (104) connected in the positive direction of the x-axis and the y-axis, and two straight-moving sliders ( 118) are respectively installed on the lead screws of the X-axis lead screw stepper motor (108) and the Y-axis lead screw stepper motor (109) through the anti-backlash lead screw nut (119), driven by the lead screws of the two stepper motors The straight-moving slider (118) performs linear motion up and down to drive the laser mirror (101) to rotate around the x-axis and the y-axis. On the other two motor brackets (104), counterweights (117) are installed to satisfy the static and dynamic balance when the laser reflector (101) rotates around three axes. The central column (107) is firmly connected with the central column chassis (115) to maintain a vertical relationship. The lower stepped shaft of the center column (107) passes through the miniature ball bearing (111), and is connected with the z-axis stepping motor (112) through a shaft coupling. When the z-axis stepping motor (112) rotates, it can drive the center column (107) to rotate. The four motor brackets (104) are respectively fixedly connected to the four longitudinal deflection hinges (116), which can realize the micro deflection of the four motor brackets (104) along the direction perpendicular to the corresponding sides of the connected laser mirror (101). At the same time, the four longitudinal deflection hinges (116) are respectively connected with the four axial deflection hinges (110), so that the four motor brackets (104) can be slightly moved along the direction parallel to the corresponding side of the connected laser reflector (101). deflection.

Wherein, the structural characteristics of the laser scanning attitude angle stabilizing device (1) can meet the requirements of installing a larger-sized laser mirror (101) while maintaining a smaller device volume and mass. The specific size of the laser reflector (101) used is 100mm×100mm×2mm.

Among them, the laser reflector (101) is installed on the cross-shaped mirror support rod (102), and the four rod ends of the cross-shaped mirror support rod (102) are a square joint with threaded holes, which can be connected with the ball head. Connect to the screw end of the bearing (103). Then the threaded hole end of the ball joint universal bearing (103) is connected with the screw end of the straight-moving slider (118), and the straight-moving slider (118) is consolidated with the anti-backlash screw nut (119), and the The bar is driven by a stepper motor to move up and down. The cross-shaped mirror support rod (102) is fixedly connected with a small slotted stainless steel hemisphere (105). The slotted stainless steel small hemisphere (105) is a small half steel ball part cut off from a solid steel ball with a diameter of 30mm at a position 2mm away from the center of the ball, and the center of the cross-shaped mirror support rod (102) is processed on the cutting plane. Cross-shaped grooves with the same size, so that the cross-shaped mirror support rod (102) can be firmly embedded in the center of the grooved stainless steel small hemisphere (105), and bonded tightly. Paste the laser reflector (101) on the cross-shaped mirror support bar (102), so that it can be ensured that the rotation center of the laser reflector (101) coincides with the spherical center of the slotted stainless steel hemisphere (105). A magnetic steel concave spherical body (106) made of a magnetic steel material is firmly connected with the central column (107). The slotted stainless steel small hemisphere (105) and the magnetic steel concave spherical body (106) are tightly attracted by the force of the magnetic field. No relative displacement occurs, only spherical sliding contact is formed. Through magnetic attraction, the two isolated parts of the slotted stainless steel small hemisphere (105) and the magnetic steel concave spherical body (106) can be combined into a magnetic universal motion bearing structure. Simultaneously, since the thickness of the laser reflector (101) is 2 mm, which is just equal to the distance of the grooved stainless steel hemisphere (105) from the ball point, the laser reflector (101) is pasted on the cross-shaped mirror surface support bar (102). , the laser reflection center point of the laser reflector (101) will coincide with the center of the grooved stainless steel small hemisphere (105), so that the rotation center of the laser reflector (101) can be fixed when it rotates. When the laser pulse is reflected at the rotation center of the laser reflector (101), the scanning center point of the outgoing laser pulse beam also remains unchanged.

Wherein, the rotation of the laser reflector (101) around the x and y axes adopts the lead screw and anti-backlash lead screw nut (119) of the X-axis lead screw stepping motor (108) and the Y-axis lead screw stepping motor (109) respectively. The mechanism drives the straight-moving slider (118) to move up and down; the rotation of the laser mirror (101) around the z-axis is directly driven by a z-axis stepping motor (112). The screw stepping motor is to replace the rotating shaft of the stepping motor with a longer screw, and add an internal thread slider on the screw that can be driven by external force, and form an engagement between the internal thread and the screw. In this way, the purpose of the slider moving linearly along the axial direction is achieved. The screw nut is a mechanical subdivision structure, which can achieve different control accuracy by controlling the pitch of the thread. The Y-axis lead screw stepping motor (109) is fixedly installed in the motor bracket (104), and the anti-backlash lead screw nut (119) installed on the lead screw is fixedly connected with the straight-moving slider (118) installed thereon, The straight-moving slider (118) is connected with the screw hole end of the ball joint bearing (103) through the small screw rod protruding from the front side, and the small screw rod protruding from the other end of the ball joint bearing (103) is connected with the cross-shaped The rod end of the mirror surface support rod (102) is connected with screw holes, so when the Y-axis screw stepping motor (109) rotates, it can drive the anti-backlash screw nut (119), the direct moving slider (118), the ball The head universal bearing (103), the cross-shaped mirror support rod (102), and the laser reflector (101) rotate around the X axis. The optical axis extends vertically from both sides of the linear slider (118), and the optical axis is firmly connected with the inner ring of the miniature bearing, and the outer ring of the miniature bearing is placed in the track groove on the side of the motor bracket (104). The constraint can eliminate the radial rotation of the linear slider (118) with the screw rod under the action of frictional resistance, so that it can only move linearly along the axial direction of the screw rod, and the rolling contact is formed between the miniature bearing and the track groove wall, reducing The frictional resistance of the track groove to the straight slide block (118) has been improved. A longitudinal deflection hinge (116) is installed at the bottom center of the motor support (104), and the longitudinal deflection hinge (116) is connected with the axial deflection hinge (110). The axial deflection hinge (110) has a certain damping and spring restoring force, and when the laser reflector (101) is perpendicular to the center column (107), it can maintain the motor support (104) parallel to the center column; and when the screw rod When the stepping motor drives the laser reflector to rotate, the motor bracket (104) can be slightly deflected in the two hinge rotation directions according to the geometric structure constraints of the device. The center column chassis (115) is tightly connected with the center column (107) through interference fit. In the motor bracket (104) on the direction opposite to the Y-axis lead screw stepper motor (109), a counterweight (117) equal in quality to the Y-axis lead screw stepper motor (109) is installed to realize the laser reflector ( 101) Dynamic and static balance during rotation. The relevant structure and working mode of the X-axis lead screw stepper motor (109) are the same as the Y-axis lead screw stepper motor (109).

Among them, the central column (107) is designed in the shape of a stepped shaft, which is divided into four stages, and these four parts are arranged in descending order of their diameters: the first part serves as the central support shaft of the entire laser reflector (101), and The magnetic steel concave spherical body (106) is fastened and welded; the second part forms an interference fit with the center hole of the center column chassis (115), and utilizes the huge bonding force to make the center column (107) and the center column chassis (115) become One piece; the third part is installed on the miniature ball bearing (111) in the center hole of the installation base (114), and the stepped shaft is fitted together with the inner ring of the miniature ball bearing (111); the fourth part passes through the miniature ball bearing The bearing (111) is connected with the rotating shaft of the z-axis stepping motor (112) through a shaft coupling, so as to realize the rotational drive around the z-axis. The mounting base (114) is square, and support columns (113) are installed on its four corners respectively, which can further be fixedly connected with the airborne platform (5).

为安装x轴丝杠步进电机（108）的电机支架（104）相对于垂直方向的微小倾斜角。由Px₁’和Px₂两点之间的距离，根据勾股定理，可建立丝杠上的直动滑块（118）移动量△x与激光反射镜（101）的旋转角度θ之间的关系：Among them, when the laser reflector (101) only rotates around the single axis of the x-axis or the y-axis, such as rotating around the y-axis, it is assumed that when the X-axis screw stepping motor (108) rotates, the linear axis on the screw When the center point of the movable slider (118) has moved a distance of Δx, the laser reflector (101) has rotated an angle of θ around the y-axis. The set point o is the center of symmetry of the laser mirror (101), px ₁ is the center of rotation of the ball joint bearing (103) on the x-axis, px ₂ is the center of rotation of the longitudinal deflection hinge (116) on the x-axis, px ₃ is the center of motion of the straight slide block (118) on the x-axis. px ₁ ' is the spatial position of the rotation center of the ball joint universal bearing (103) on the x-axis when the rotation angle of the laser reflection mirror (101) is θ, and px ₃ ' is when the rotation angle of the laser reflection mirror (101) is θ, also That is, the motion center point after the straight-moving slide block (118) moves up and down by △x distance on the x-axis.

For installing the motor bracket (104) of the x-axis lead screw stepper motor (108) with respect to the slight inclination angle of the vertical direction. From the distance between the two points Px ₁ ' and Px ₂ , according to the Pythagorean theorem, the relationship between the movement amount △x of the straight-moving slider (118) on the lead screw and the rotation angle θ of the laser mirror (101) can be established relation:

（1）

(1)

Solutions have to:

（2）

(2)

When r1=7, r2=3.7, d1=14,

（3）

(3)

（4）

(4)

，然后再绕y轴转动

，设此时x轴丝杆步进电机（109）上的直动滑块（118）移动△x，而y轴丝杆步进电机（109）上的直动滑块（118）移动△y，分析两个丝杠上的直动滑块（118）的移动距离与激光反射镜（101）的两个转角之间的对应关系。设Py₁是y轴上球头万向轴承（103）的转动中心点，py₂是y轴上纵向偏转铰链（116）的转动中心点，py₃是y轴上直动滑块（118）的运动中心点。激光反射镜（101）绕两轴的转动过程中，py₁与py₃连线始终平行于y轴方向，py₁与py₃的连线始终垂直于py₂与py₃的连线，此时，py₂与py₃连线绕点py₂既有沿着平行于y轴方向的微小转动，又有沿着平行于x轴方向的微小转动。而对于x轴，px₂与px₃连线绕点px₂只有沿着平行于x轴方向的微小转动，而在沿着平行于y轴的方向上没有微小转动。这是激光反射镜（101）绕两轴都转动时、先控制Y轴丝杆步进电机（109）移动再控制X轴丝杆步进电机（108）移动带来的两轴电机支架（104）的中心轴倾斜角的不同之处。因此，在结构设计上，在py₂处要有一个围绕y轴方向转动的轴向偏转铰链（110），同时有能绕沿着平行于x轴方向转动的纵向偏转铰链（116）。而在px₂处，只要有一个绕沿着x轴方向转动的纵向偏转铰链（116）即可，其轴上的轴向偏转铰链（110）可以锁死在铅锤方向上而不用转动。When the laser mirror (101) rotates around the x-axis and the y-axis, for example, the laser mirror (101) first rotates an angle around the x-axis

, and then rotate around the y-axis

, it is assumed that the linear slider (118) on the x-axis screw stepper motor (109) moves △x, and the linear slider (118) on the y-axis screw stepper motor (109) moves △y , analyzing the corresponding relationship between the moving distance of the linear sliding block (118) on the two lead screws and the two rotation angles of the laser mirror (101). Let Py ₁ be the center of rotation of the ball joint bearing (103) on the y-axis, py ₂ be the center of rotation of the longitudinal deflection hinge (116) on the y-axis, and py ₃ be the straight-moving slider (118) on the y-axis center of motion. During the rotation of the laser mirror (101) around the two axes, the line connecting py ₁ and py ₃ is always parallel to the y-axis direction, and the line connecting py ₁ and py ₃ is always perpendicular to the line connecting py ₂ and py _3. At this time , the line connecting py ₂ and py ₃ around the point py ₂ not only has a small rotation along the direction parallel to the y-axis, but also has a small rotation along the direction parallel to the x-axis. As for the x-axis, the line connecting px ₂ and px ₃ around the point px ₂ only has a slight rotation along the direction parallel to the x-axis, but there is no slight rotation along the direction parallel to the y-axis. This is when the laser reflector (101) rotates around both axes, first controlling the Y-axis screw stepping motor (109) to move and then controlling the X-axis screw stepping motor (108) to move the two-axis motor support (104) ) The difference in the inclination angle of the central axis. Therefore, in terms of structural design, there should be an axial deflection hinge (110) that can rotate around the y-axis direction at py ₂ , and a longitudinal deflection hinge (116) that can rotate around the direction parallel to the x-axis. And at px ₂ , as long as there is a longitudinal deflection hinge (116) that rotates along the x-axis direction, the axial deflection hinge (110) on the shaft can be locked in the plumb direction without rotation.

（5）

(5)

（6）

(6)

That is, a one-to-one correspondence is established between the two displacements of the straight-moving slider (118) on the X and Y axis stepping motor lead screws and the two rotation angles of the laser mirror (101) around the X and Y axes.

Wherein, the rotation of the laser mirror (101) around the z-axis is relatively independent, as long as the z-axis stepping motor is controlled to rotate, there will be no coupling effect on the rotation around the x-axis and the y-axis.

（θ-ω/2+ω_e），绕y轴的总转动角度为

（φ_e-φ/2），绕z轴的总转动角度为（γ_e-γ）。根据式（5）和（6），可得相应的丝杠直动滑块位移△x和△y，以及绕z轴的转动控制角度（γ_e-γ）。Among them, the three-dimensional rotation angle of the laser mirror (101) is the synthesis of three movements, one is the swing scanning angle around the x-axis, which is set to θ; the other is the change of the three-dimensional attitude angle of the airborne platform (ω, φ, γ) Compensation, respectively (-ω/2, -φ/2, -γ); the third is to let the normal direction of the laser reflector (101) point to any direction in space, and set the normal of the desired laser reflector (101) The three attitude angles of the direction relative to the initial attitude position are (ω _e , φ _e , γ _e ), then the total rotation angle of the laser mirror (101) around the x-axis is

(θ-ω/2+ω _e ), the total rotation angle around the y-axis is

(φ _e -φ/2), the total rotation angle around the z axis is (γ _e -γ). According to formulas (5) and (6), the displacements △x and △y of the linear motion slider of the lead screw can be obtained, as well as the rotation control angle (γ _e - γ) around the z-axis.

Among them, the attitude angle stabilization device controller adopts an embedded control system, and there are three driving parts to be controlled: the x-axis screw stepping motor (108), the y-axis screw stepping motor (109) and the z-axis stepping motor Motor (112); there are six external information to be received: three attitude angles of the airborne platform (5), namely roll angle, pitch angle and yaw angle; three attitude angles of the laser reflector (101). Use the embedded system S3c2440 to receive the six instantaneous attitude angle information collected by the laser gyroscope (2) and the MEMS gyroscope (4); according to the set laser scanning swing angle, the target space pointed by the normal line of the laser mirror (101) Orientation, the current six attitude angle information, calculate the rotation angle (γ _e -γ) of the △x, △y, z axis, and obtain the number of rotation steps of the stepping motor on each axis; finally, use the output interface to control the 3 a stepping motor driver to drive the laser reflector (101) to rotate to the specified three rotation angles.

Among them, the control system software program of the attitude angle stabilization device controller includes: (1) Bootstrap program: complete the establishment of the abnormal interrupt vector table, close the watchdog timer, initialize the system clock, and initialize the general-purpose input/output interface (GPIO) , Each PWM timer initialization, interrupt initialization and other work. (2) I ² C data acquisition program: when the attitude angle stabilization device starts to work, first judge the running status of the three stepping motors. If the three stepping motors are all in a stalled state, configure the I ² C interface as the main receiving mode to receive the three-axis attitude angle data measured by the laser gyroscope (2) and the MEMS gyroscope (4). (3) Calculation program for the number of motor rotation steps: the step angle of the selected screw stepper motor is 1.8°, so the motor needs 200 steps to complete the 360° rotation. If the screw lead is 5.08mm, the motion step of the anti-backlash screw nut (119) of the motor is 0.0254mm, and the resolution of the rotation angle control of the laser mirror (101) is 0.029°. In this way, the angle control resolution of the laser mirror can be halved, that is, 0.0145°. (4) Motor operation program: the rotation of the three stepper motors is driven by three groups of GPIO pins to control their stepper motor drivers, and the steering of the x-axis screw stepper motor (108) is controlled by the level signal provided by GPG3. The rotation angle is controlled by the pulse signal provided by GPE11; the steering of the y-axis screw stepper motor (109) is controlled by the level signal provided by GPG5, and the rotation angle is controlled by the pulse signal provided by GPE12; the z-axis stepper motor (112) The steering is controlled by the level signal provided by GPG6, and the rotation angle is controlled by the pulse signal provided by GPE13.

Description of drawings

Figure 1 is a schematic diagram of the attitude angle stabilization of the laser scanning achieved by the helicopter-borne LiDAR.

Figure 2 is a composition diagram of the airborne LiDAR attitude angle stabilization system.

Fig. 3 is a mechanical structure diagram of the laser scanning attitude angle stabilization device (1).

Fig. 4 is a related structural diagram of the laser reflector (101).

Fig. 5 is a structural diagram of the drive mechanism of the screw stepper motor.

Fig. 6 is a z-axis driving structure diagram of the central column (107).

Fig. 7 is an analysis diagram of the control principle that the laser reflector (101) only rotates around the Y axis.

Fig. 8 is an analysis diagram of the control principle of the rotation of the laser mirror (101) around the X-axis and the Y-axis.

Fig. 9 is a schematic structural diagram of the control system of the controller of the attitude angle stabilization device.

Fig. 10 is a flow chart of the control system program of the attitude angle stabilizing device controller.

detailed description

The patent embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Figure 1 is a schematic diagram of the attitude angle stabilization of the laser scanning achieved by the helicopter-borne LiDAR. The laser pulse emitter (3) is consolidated with the airborne platform (5), and the laser emission direction points to the geometric center of the laser reflector (101) and shoots to the measured ground. The base of the laser reflector (101) is consolidated with the airborne platform (5), and the laser reflector (101) reflects the laser pulse beam at a fixed angle so that the laser pulse beam points to a certain spatial direction. When the laser radar is working, it is usually expected that the outgoing spatial direction of the laser pulse beam remains unchanged, but the attitude angle of the airborne platform (5) changes at any time, causing the outgoing direction of the laser pulse to deviate from the expected direction. XYZ-O is a Cartesian coordinate system, the X direction is the forward direction of the flight, the Z direction is vertically downward, and the Y direction is perpendicular to X and Z, and satisfies the right-hand rule. When the airborne platform (5) has a clockwise pitch angle of 2α around the Y axis, the outgoing laser direction is shifted, so if the outgoing direction is to be kept unchanged, the laser reflector (101) needs to be rotated counterclockwise on the airborne platform (5) Half of the pitch angle, ie α. For roll angle compensation, the method is the same. Therefore, in the direction of pitch angle and roll angle, by reversely rotating the laser reflector (101) half of the value of the corresponding attitude angle, the angle of the outgoing light can be corrected to an ideal situation without attitude angle disturbance. However, the perturbation of the yaw angle of the airborne platform (5) only rotates the direction of the laser emission angle around the z-axis without changing the emission angle. Therefore, when the yaw angle of the airborne platform (5) has a rotation angle, only Turn the scan mirror in reverse by the same angle as the yaw angle.

Figure 2 is a composition diagram of the airborne LiDAR attitude angle stabilization system. It can realize the airborne LiDAR laser scanning attitude angle stabilization system, including laser scanning attitude angle stabilization device (1), laser gyroscope (2), laser pulse emitter (3), MEMS gyroscope (4), airborne platform (5) ). The laser scanning attitude angle stabilizing device (1) includes a mechanical transmission part and an attitude angle stabilizing device controller. The reference coordinate system is XYZ-o, where the X direction is the forward direction of the aircraft, Z is the vertical downward direction, and Y is the right direction of the aircraft. The coordinate origin o is the laser scanning optical center, that is, the rotation center of the laser mirror (101), that is, the laser pulse reflection point of the laser mirror (101). The laser pulse emitter (3) is consolidated with the airborne platform (5), and the laser emission direction points to the center of the laser reflector (101) and shoots to the measured ground. The laser gyroscope (2) is used to measure the attitude angle change of the airborne platform (5) in real time, and the laser reflector (101) is controlled to rotate accordingly, so as to stabilize the spatial direction of the laser scanning output. In addition, the MEMS gyroscope (4) is installed on the back of the laser reflector (101) for measuring the actual three-dimensional attitude angle of the laser reflector (101). By comparing the measured values of the laser gyroscope (2) and the MEMS gyroscope (4), the angle difference between the two is obtained, and the center normal of the laser reflector (101) can be controlled to point to any desired spatial orientation. Laser tracking scanning and detection of dynamic and static targets. On the other hand, when the airborne platform (5) has a three-dimensional attitude angle change, control the x-axis and y-axis of the laser mirror (101) to reversely rotate the roll angle and pitch angle of the airborne platform (5) respectively. half of the value, and the z-axis reversely rotates with the same amplitude as the yaw angle measurement value of the airborne platform (5), so that the spatial orientation of the laser beam emitted after being reflected by the laser reflector (101) is not random. The influence of the three-dimensional attitude angle change of the carrying platform (5). At the same time, the laser reflector (101) also needs to realize the laser scanning function. Therefore, the control movement of the laser mirror (101) is the superposition of three control signals, one is the scanning and swinging movement around the x-axis to realize the laser two-dimensional scanning; the other is the real-time change of the three-dimensional attitude angle of the airborne platform (5). compensation movement; the third is that the laser reflector (101) normal points to realize the real-time tracking movement of the space dynamic target.

Fig. 3 is a mechanical structure diagram of the laser scanning attitude angle stabilization device (1). The mechanical transmission part of the laser scanning attitude angle stabilization device (1) includes: laser reflector (101), cross-shaped mirror support rod (102), ball joint universal bearing (103), motor bracket (104), slotted stainless steel small Hemisphere (105), magnetic steel concave spherical body (106), central column (107), x-axis screw stepping motor (108), y-axis screw stepping motor (109), axial deflection hinge (110) , miniature ball bearing (111), z-axis stepper motor (112), support column (113), mounting base (114), center column chassis (115), longitudinal deflection hinge (116), counterweight (117), Straight moving slider (118), anti-backlash lead screw nut (119). The laser reflector (101) can realize three-axis rotation, and the coordinate origin o of the reference coordinate system XYZ-o is the symmetry center of the laser reflector (101), that is, the rotation center of the laser reflector and the laser pulse reflection point. The mirror symmetry center of the laser reflector (101) coincides with the rotation center of the laser reflector (101), and its spatial position is fixed by a central column (107). The x-axis and y-axis in the two directions of the two mutually perpendicular sides of the laser reflector (101) are respectively the rotation axes of the roll angle (x-axis) and the pitch angle (y-axis) of the airborne platform, which can be stepped by the x-axis screw The motor (108) and the y-axis screw stepper motor (109) respectively drive the laser mirror (101) to rotate around the y-axis and the x-axis. The center column (107) can rotate around the z-axis, which is the same as the rotation axis of the yaw angle. The z-axis stepping motor (112) fixed on the installation base (114) drives the center column (107) to rotate, thereby driving The laser reflector (101) rotates around the z axis.

The center of the mirror surface and the midpoints of the four sides of the mirror surface of the laser reflector (101) are control points for constraining the rotation orientation of the mirror surface in space. The four linear slides (118) are connected by ball joint bearings (103). Rolling bearings are installed at the two ends of the four straight-moving slide blocks (118), which can move up and down along the track grooves of the four motor supports (104) respectively. The X-axis lead screw stepper motor (108) and the Y-axis lead screw stepper motor (109) are respectively installed in the two motor brackets (104) connected in the positive direction of the x-axis and the y-axis, and two straight-moving sliders ( 118) are respectively installed on the lead screws of the X-axis lead screw stepper motor (108) and the Y-axis lead screw stepper motor (109) through the anti-backlash lead screw nut (119), driven by the lead screws of the two stepper motors The straight-moving slider (118) performs linear motion up and down to drive the laser mirror (101) to rotate around the x-axis and the y-axis. On the other two motor brackets (104), counterweights (117) are installed to satisfy the static and dynamic balance when the laser reflector (101) rotates around three axes. The central column (107) is firmly connected with the central column chassis (115) to maintain a vertical relationship. The lower stepped shaft of the center column (107) passes through the miniature ball bearing (111), and is connected with the z-axis stepping motor (112) through a shaft coupling. When the z-axis stepping motor (112) rotates, it can drive the center column (107) to rotate. The four motor brackets (104) are respectively fixedly connected to the four longitudinal deflection hinges (116), which can realize the micro deflection of the four motor brackets (104) along the direction perpendicular to the corresponding sides of the connected laser mirror (101). At the same time, the four longitudinal deflection hinges (116) are respectively connected with the four axial deflection hinges (110), so that the four motor brackets (104) can be slightly moved along the direction parallel to the corresponding side of the connected laser reflector (101). deflection.

For airborne LiDAR, a correct recording can only be made if the received echo signal is strong enough. As the detection distance increases, the echo signal that can be received by the mirror becomes weaker, and it is necessary to increase the size of the laser mirror (101) to reflect as many echo signals as possible. In the structure of the traditional attitude angle stabilized platform using a three-axis rotating platform, the size of the scanning mirror is severely limited. However, the structural characteristics of the laser scanning attitude angle stabilization device (1) can meet the requirements of installing a larger-sized laser mirror (101) while maintaining a smaller device volume and mass. The specific size of the laser reflector (101) used in this device is 100mm×100mm×2mm.

Fig. 4 is a related structural diagram of the laser reflector (101). The laser reflector (101) is installed on the cross-shaped mirror support rod (102), and the four rod ends of the cross-shaped mirror support rod (102) are a square joint with threaded holes, which can be connected with the ball joint universal bearing (103) screw end is connected. Then the threaded hole end of the ball joint universal bearing (103) is connected with the screw end of the straight-moving slider (118), and the straight-moving slider (118) is consolidated with the anti-backlash screw nut (119), and the The bar is driven by a stepper motor to move up and down. The cross-shaped mirror support rod (102) is fixedly connected with a small slotted stainless steel hemisphere (105). The slotted stainless steel small hemisphere (105) is a small half steel ball part cut off from a solid steel ball with a diameter of 30mm at a position 2mm away from the center of the ball, and the center of the cross-shaped mirror support rod (102) is processed on the cutting plane. Cross-shaped grooves with the same size, so that the cross-shaped mirror support rod (102) can be firmly embedded in the center of the grooved stainless steel small hemisphere (105), and bonded tightly. Paste the laser reflector (101) on the cross-shaped mirror support bar (102), so that it can be ensured that the rotation center of the laser reflector (101) coincides with the spherical center of the slotted stainless steel hemisphere (105). A magnetic steel concave spherical body (106) made of a magnetic steel material is firmly connected with the central column (107). The slotted stainless steel small hemisphere (105) and the magnetic steel concave spherical body (106) are tightly attracted by the force of the magnetic field. No relative displacement occurs, only spherical sliding contact is formed. Through magnetic attraction, the two isolated parts of the slotted stainless steel small hemisphere (105) and the magnetic steel concave spherical body (106) can be combined into a magnetic universal motion bearing structure. Simultaneously, since the thickness of the laser reflector (101) is 2 mm, which is just equal to the distance of the grooved stainless steel hemisphere (105) from the ball point, the laser reflector (101) is pasted on the cross-shaped mirror surface support bar (102). , the laser reflection center point of the laser reflector (101) will coincide with the center of the grooved stainless steel small hemisphere (105), so that the rotation center of the laser reflector (101) can be fixed when it rotates. When the laser pulse is reflected at the rotation center of the laser reflector (101), the scanning center point of the outgoing laser pulse beam also remains unchanged.

Figure 5 is a structural diagram of the drive mechanism of the screw stepping motor. The rotation of the laser mirror (101) around the x and y axes adopts the screw rod and anti-backlash screw nut (119) mechanism of the X-axis screw stepping motor (108) and the Y-axis screw stepping motor (109), respectively, Drive the straight-moving slider (118) to move up and down; the rotation of the laser mirror (101) around the z-axis is directly driven by a z-axis stepping motor (112). The screw stepping motor is to replace the rotating shaft of the stepping motor with a longer screw, and add an internal thread slider on the screw that can be driven by external force, and form an engagement between the internal thread and the screw. In this way, the purpose of the slider moving linearly along the axial direction is achieved. The screw nut is a mechanical subdivision structure, which can achieve different control accuracy by controlling the pitch of the thread. The Y-axis lead screw stepping motor (109) is fixedly installed in the motor bracket (104), and the anti-backlash lead screw nut (119) installed on the lead screw is fixedly connected with the straight-moving slider (118) installed thereon, The straight-moving slider (118) is connected with the screw hole end of the ball joint bearing (103) through the small screw rod protruding from the front side, and the small screw rod protruding from the other end of the ball joint bearing (103) is connected with the cross-shaped The rod end of the mirror surface support rod (102) is connected with screw holes, so when the Y-axis screw stepping motor (109) rotates, it can drive the anti-backlash screw nut (119), the direct moving slider (118), the ball The head universal bearing (103), the cross-shaped mirror support rod (102), and the laser reflector (101) rotate around the X axis. The optical axis extends vertically from both sides of the linear slider (118), and the optical axis is firmly connected with the inner ring of the miniature bearing, and the outer ring of the miniature bearing is placed in the track groove on the side of the motor bracket (104). The constraint can eliminate the radial rotation of the linear slider (118) with the screw rod under the action of frictional resistance, so that it can only move linearly along the axial direction of the screw rod, and the rolling contact is formed between the miniature bearing and the track groove wall, reducing The frictional resistance of the track groove to the straight slide block (118) has been improved. A longitudinal deflection hinge (116) is installed at the bottom center of the motor support (104), and the longitudinal deflection hinge (116) is connected with the axial deflection hinge (110). The axial deflection hinge (110) has a certain damping and spring restoring force, and when the laser reflector (101) is perpendicular to the center column (107), it can maintain the motor support (104) parallel to the center column; and when the screw rod When the stepping motor drives the laser reflector to rotate, the motor bracket (104) can be slightly deflected in the two hinge rotation directions according to the geometric structure constraints of the device. The center column chassis (115) is tightly connected with the center column (107) through interference fit. In the motor bracket (104) on the direction opposite to the Y-axis lead screw stepper motor (109), a counterweight (117) equal in quality to the Y-axis lead screw stepper motor (109) is installed to realize the laser reflector ( 101) Dynamic and static balance during rotation. The relevant structure and working mode of the X-axis lead screw stepper motor (109) are the same as the Y-axis lead screw stepper motor (109).

Fig. 6 is a z-axis driving structural diagram of the central column (107). The central column (107) is designed in the shape of a stepped shaft, which is divided into four stages, and these four parts are arranged in descending order of their diameters: the first part is the central support shaft of the entire laser reflector (101), and the magnetic steel The concave spherical body (106) is fastened and welded; the second part forms an interference fit with the center hole of the center column chassis (115), and utilizes a huge bonding force to make the center column (107) and the center column chassis (115) into one; The third part is installed on the miniature ball bearing (111) in the center hole of the mounting base (114), and the stepped shaft is fitted together with the inner ring of the miniature ball bearing (111) with interference fit; the fourth part passes through the miniature ball bearing ( 111), which is connected with the rotating shaft of the z-axis stepping motor (112) through a coupling to realize the rotation drive around the z-axis. The mounting base (114) is square, and support columns (113) are installed on its four corners respectively, which can further be fixedly connected with the airborne platform (5).

为安装x轴丝杠步进电机（108）的电机支架（104）相对于垂直方向的微小倾斜角。由Px₁’和Px₂两点之间的距离，根据勾股定理，可建立丝杠上的直动滑块（118）移动量△x与激光反射镜（101）的旋转角度θ之间的关系：Fig. 7 is an analysis diagram of the control principle of the laser reflector (101) only rotating around the Y axis. When the laser reflector (101) only rotates around the x-axis or the y-axis, such as around the y-axis, when the X-axis screw stepper motor (108) rotates, the linear slide on the screw When the central point of the block (118) has moved a distance of Δx, the laser reflector (101) has rotated an angle of θ around the y-axis. The set point o is the center of symmetry of the laser mirror (101), px ₁ is the center of rotation of the ball joint bearing (103) on the x-axis, px ₂ is the center of rotation of the longitudinal deflection hinge (116) on the x-axis, px ₃ is the center of motion of the straight slide block (118) on the x-axis. px ₁ ' is the spatial position of the rotation center of the ball joint universal bearing (103) on the x-axis when the rotation angle of the laser reflection mirror (101) is θ, and px ₃ ' is when the rotation angle of the laser reflection mirror (101) is θ, also That is, the motion center point after the straight-moving slide block (118) moves up and down by △x distance on the x-axis.

For installing the motor bracket (104) of the x-axis lead screw stepper motor (108) with respect to the slight inclination angle of the vertical direction. From the distance between the two points Px ₁ ' and Px ₂ , according to the Pythagorean theorem, the relationship between the movement amount △x of the straight-moving slider (118) on the lead screw and the rotation angle θ of the laser mirror (101) can be established relation:

（1）

(1)

Solutions have to:

（2）

(2)

When r1=7, r2=3.7, d1=14,

（3）

(3)

（4）

(4)

，然后再绕y轴转动

，设此时x轴丝杆步进电机（109）上的直动滑块（118）移动△x，而y轴丝杆步进电机（109）上的直动滑块（118）移动△y，分析两个丝杠上的直动滑块（118）的移动距离与激光反射镜（101）的两个转角之间的对应关系。设Py₁是y轴上球头万向轴承（103）的转动中心点，py₂是y轴上纵向偏转铰链（116）的转动中心点，py₃是y轴上直动滑块（118）的运动中心点。激光反射镜（101）绕两轴的转动过程中，py₁与py₃连线始终平行于y轴方向，py₁与py₃的连线始终垂直于py₂与py₃的连线，此时，py₂与py₃连线绕点py₂既有沿着平行于y轴方向的微小转动，又有沿着平行于x轴方向的微小转动。而对于x轴，px₂与px₃连线绕点px₂只有沿着平行于x轴方向的微小转动，而在沿着平行于y轴的方向上没有微小转动。这是激光反射镜（101）绕两轴都转动时、先控制Y轴丝杆步进电机（109）移动再控制X轴丝杆步进电机（108）移动带来的两轴电机支架（104）的中心轴倾斜角的不同之处。因此，在结构设计上，在py2处要有一个围绕y轴方向转动的轴向偏转铰链（110），同时有能绕沿着平行于x轴方向转动的纵向偏转铰链（116）。而在px₂处，只要有一个绕沿着x轴方向转动的纵向偏转铰链（116）即可，其轴上的轴向偏转铰链（110）可以锁死在铅锤方向上而不用转动。Fig. 8 is an analysis diagram of the control principle of the rotation of the laser mirror (101) around the X-axis and the Y-axis. When the laser mirror (101) rotates around the x-axis and the y-axis, for example, the laser mirror (101) first rotates an angle around the x-axis

, and then rotate around the y-axis

, it is assumed that the linear slider (118) on the x-axis screw stepper motor (109) moves △x, and the linear slider (118) on the y-axis screw stepper motor (109) moves △y , analyzing the corresponding relationship between the moving distance of the linear sliding block (118) on the two lead screws and the two rotation angles of the laser mirror (101). Let Py ₁ be the center of rotation of the ball joint bearing (103) on the y-axis, py ₂ be the center of rotation of the longitudinal deflection hinge (116) on the y-axis, and py ₃ be the straight-moving slider (118) on the y-axis center of motion. During the rotation of the laser mirror (101) around the two axes, the line connecting py ₁ and py ₃ is always parallel to the y-axis direction, and the line connecting py ₁ and py ₃ is always perpendicular to the line connecting py ₂ and py _3. At this time , the line connecting py ₂ and py ₃ around the point py ₂ not only has a small rotation along the direction parallel to the y-axis, but also has a small rotation along the direction parallel to the x-axis. As for the x-axis, the line connecting px ₂ and px ₃ around the point px ₂ only has a slight rotation along the direction parallel to the x-axis, but there is no slight rotation along the direction parallel to the y-axis. This is when the laser reflector (101) rotates around both axes, first controlling the Y-axis screw stepping motor (109) to move and then controlling the X-axis screw stepping motor (108) to move the two-axis motor support (104) ) The difference in the inclination angle of the central axis. Therefore, in terms of structural design, there must be an axial deflection hinge (110) that rotates around the y-axis direction at py2, and a longitudinal deflection hinge (116) that can rotate around the direction parallel to the x-axis. And at px ₂ , as long as there is a longitudinal deflection hinge (116) that rotates along the x-axis direction, the axial deflection hinge (110) on the shaft can be locked in the plumb direction without rotation.

（5）

(5)

（6）

(6)

That is, a one-to-one correspondence is established between the two displacements of the straight-moving slider (118) on the X and Y axis stepping motor lead screws and the two rotation angles of the laser mirror (101) around the X and Y axes.

The rotation of the laser reflector (101) around the z-axis is relatively independent, as long as the z-axis stepping motor is controlled to rotate, there will be no coupling effect on the rotation around the x-axis and the y-axis.

（θ-ω/2+ω_e），绕y轴的总转动角度为

（φ_e-φ/2），绕z轴的总转动角度为（γ_e-γ）。根据式（5）和（6），可得相应的丝杠直动滑块位移△x和△y，以及绕z轴的转动控制角度（γ_e-γ）。The three-dimensional rotation angle of the laser mirror (101) is the synthesis of three movements, one is the swing scanning angle around the x-axis, which is set to θ; the other is the compensation for the three-dimensional attitude angle change (ω, φ, γ) of the airborne platform , respectively (-ω/2, -φ/2, -γ); the third is to let the normal direction of the laser mirror (101) point to any direction in space, and set the desired normal direction of the laser mirror (101) The three attitude angles relative to the initial attitude position are (ω _e , φ _e , γ _e ), then the total rotation angle of the laser mirror (101) around the x-axis is

(θ-ω/2+ω _e ), the total rotation angle around the y-axis is

(φ _e -φ/2), the total rotation angle around the z axis is (γ _e -γ). According to formulas (5) and (6), the displacements △x and △y of the linear motion slider of the lead screw can be obtained, as well as the rotation control angle (γ _e - γ) around the z-axis.

Fig. 9 is a schematic structural diagram of the control system of the controller of the attitude angle stabilization device. The attitude angle stabilizer controller adopts an embedded control system, and there are three driving parts to be controlled: the x-axis screw stepping motor (108), the y-axis screw stepping motor (109) and the z-axis stepping motor ( 112); there are six external information to be received: three attitude angles of the airborne platform (5), namely roll angle, pitch angle and yaw angle; three attitude angles of the laser reflector (101). Use the embedded system S3c2440 to receive the six instantaneous attitude angle information collected by the laser gyroscope (2) and the MEMS gyroscope (4); according to the set laser scanning swing angle, the target space pointed by the normal line of the laser mirror (101) Orientation, the current six attitude angle information, calculate the rotation angle (γ _e -γ) of the △x, △y, z axis, and obtain the number of rotation steps of the stepping motor on each axis; finally, use the output interface to control the 3 a stepping motor driver to drive the laser reflector (101) to rotate to the specified three rotation angles.

Fig. 10 is a flow chart of the control system program of the attitude angle stabilizer controller. The control system software program of the attitude angle stabilizer controller includes: (1) Bootstrap program: complete the establishment of the abnormal interrupt vector table, close the watchdog timer, initialize the system clock, initialize the general-purpose input/output interface (GPIO), PWM timer initialization, interrupt initialization and other work. (2) I ² C data acquisition program: When the attitude angle stabilization device starts to work, first judge the running status of the three stepping motors. If the three stepping motors are all in a stalled state, configure the I ² C interface as the main receiving mode to receive the three-axis attitude angle data measured by the laser gyroscope (2) and the MEMS gyroscope (4). (3) Calculation program for the number of motor rotation steps: the step angle of the selected screw stepper motor is 1.8°, so the motor needs 200 steps to complete a 360° rotation. If the screw lead is 5.08mm, the motion step of the anti-backlash screw nut (119) of the motor is 0.0254mm, and the resolution of the rotation angle control of the laser reflector (101) is 0.029°. The resolution of the angle control of the mirror is halved, ie 0.0145°. (4) Motor running program: The rotation of the three stepper motors is driven by three groups of GPIO pins to control their stepper motor drivers, and the steering of the x-axis screw stepper motor (108) is controlled by the level signal provided by GPG3. The rotation angle is controlled by the pulse signal provided by GPE11; the steering of the y-axis screw stepper motor (109) is controlled by the level signal provided by GPG5, and the rotation angle is controlled by the pulse signal provided by GPE12; the z-axis stepper motor (112) The steering is controlled by the level signal provided by GPG6, and the rotation angle is controlled by the pulse signal provided by GPE13.

The above description of the present invention and its specific implementations is not limited thereto, and what is shown in the accompanying drawings is only one of the implementations of the present invention. Without departing from the inventive concept of the present invention, any uninvented design of structures or embodiments similar to the technical solution shall fall within the protection scope of the present invention.

Claims (6)

1. A method for stabilizing laser scanning attitude angles of helicopter-mounted laser radars is characterized in that an attitude angle stabilizing system capable of realizing laser scanning of airborne LiDAR comprises a laser scanning attitude angle stabilizing device (1), a laser gyroscope (2), a laser pulse emitter (3), an MEMS gyroscope (4) and an airborne platform (5); the laser scanning attitude angle stabilizing device (1) comprises a mechanical transmission part and an attitude angle stabilizing device controller; the laser gyroscope (2) is adopted to measure the attitude angle change of the airborne platform (5) in real time, and a laser reflector (101) in a mechanical transmission part of the laser scanning attitude angle stabilizing device (1) is controlled to rotate correspondingly so as to stabilize the emergent space direction of a laser scanning center to be unchanged; the MEMS gyroscope (4) is arranged on the back surface of the laser reflector (101) and is used for measuring a three-dimensional attitude angle of the laser reflector (101); the angle difference between the measured values of the laser gyroscope (2) and the MEMS gyroscope (4) is obtained by comparing the measured values, the central normal of the laser reflector (101) can be controlled to point to any desired spatial orientation, and laser tracking scanning detection is carried out on dynamic and static targets; when the airborne platform (5) has three-dimensional attitude angle changeControlling the x axis and the y axis of the laser reflector (101) to respectively rotate reversely to half of the amplitude of the rolling angle and the pitch angle measured value of the airborne platform (5), and controlling the z axis to rotate reversely to the same amplitude as the amplitude of the yaw angle measured value of the airborne platform (5), so that the spatial direction of the laser beam emitted after being reflected by the laser reflector (101) is not influenced by the change of the three-dimensional attitude angle of the airborne platform (5); the laser reflector (101) swings around an x axis to realize a laser scanning function; the control movement of the laser reflector (101) is the superposition of three control signals, namely the swinging scanning movement around an x axis, so that the laser two-dimensional scanning is realized; secondly, compensating the change of the three-dimensional attitude angle of the airborne platform (5) in real time; thirdly, the normal direction of the laser reflector (101) is controlled to realize real-time tracking motion of the space dynamic target; the three-dimensional rotation angle of the laser reflector (101) is formed by synthesizing three motions, namely, swinging a scanning angle around an x axis, and setting the scanning angle as theta; secondly, compensating three-dimensional attitude angle changes (omega, phi and gamma) of the airborne platform, wherein the three-dimensional attitude angle changes are (-omega/2, -phi/2 and-gamma), and the negative sign represents reverse rotation; thirdly, the normal direction of the laser reflector (101) points to any spatial direction, and three attitude angles of the expected normal direction of the laser reflector (101) relative to the initial position of the airborne platform (5) are set as (omega) _e ，φ _e ，γ _e ) The total rotation angle of the laser mirror (101) around the x-axis is

（θ-ω/2+ω _e ) Total angle of rotation about the y-axis of

（φ _e Phi/2), total angle of rotation around the z-axis being (gamma) _e - γ); according to the mechanical motion constraint relation of the laser scanning attitude angle stabilizing device (1), the displacement delta x of the linear moving slide block on the x-axis lead screw stepping motor (109) and the displacement delta y of the linear moving slide block on the x-axis lead screw stepping motor (108) can be obtained,

，

and a rotation control angle (gamma) of the z-axis stepping motor (112) around the z-axis _e - γ); according to the formula of delta x and delta y, the angle can be rotated by a laser mirror (101)

And

reversely deducing the direct-acting displacement control quantity delta x and delta y of the screw rod stepping motors of the x axis and the y axis; the attitude angle stabilizing device controller adopts an embedded control system, and the number of the driving parts to be controlled is three: an x-axis lead screw stepping motor (108), a y-axis lead screw stepping motor (109) and a z-axis stepping motor (112); the external information to be received is six: three attitude angles of the airborne platform (5), namely a roll angle, a pitch angle and a yaw angle, and three attitude angles of the laser reflector (101); receiving six pieces of instantaneous attitude angle information acquired by a laser gyroscope (2) and an MEMS gyroscope (4) by using an embedded system S3c 2440; according to the set laser scanning swing angle, the target space direction pointed by the normal line of the laser reflector (101) and the current six attitude angle information, the rotation angles (gamma) of the delta x, delta y and z axes are calculated _e - γ) obtaining the number of steps of rotation of the stepper motor on each axis; and finally, respectively controlling 3 stepping motor drivers by using the output interface to drive the laser mirror (101) to rotate to three appointed rotation angles.

2. The method for stabilizing laser scanning attitude angle of helicopter-mounted laser radar according to claim 1, characterized in that the mechanical transmission part of said laser scanning attitude angle stabilizing device (1) comprises: the device comprises a laser reflector (101), a cross-shaped mirror support rod (102), a ball head universal bearing (103), a motor support (104), a slotted stainless steel small hemisphere (105), a magnetic steel concave sphere body (106), a central upright post (107), an x-axis screw rod stepping motor (108), a y-axis screw rod stepping motor (109), an axial deflection hinge (110), a micro ball bearing (111), a z-axis stepping motor (112), a support upright post (113), an installation base (114), a central upright post chassis (115), a longitudinal deflection hinge (116), a balancing weight (117), a direct-acting slider (118) and a backlash eliminating screw nut (119); the laser reflector (101) can realize three-axis rotation, the mirror symmetry center of the laser reflector (101) is superposed with the rotation center thereof, and the spatial position thereof is fixed by the central upright post (107); the laser reflector (101) is provided with two x-axis and y-axis which are perpendicular to each other and are respectively rotating shafts of a rolling angle and a pitching angle of an airborne platform, and the laser reflector (101) can be driven to rotate around the y-axis and the x-axis by the x-axis screw rod stepping motor (108) and the y-axis screw rod stepping motor (109) respectively; the central upright post (107) can rotate around a z-axis, the z-axis is the same as the rotation axis of the yaw angle, and the central upright post (107) is driven to rotate by the z-axis stepping motor (112) fixed on the mounting base (114), so that the laser reflector (101) is driven to rotate around the z-axis.

3. The laser scanning attitude angle stabilization method for the helicopter-borne laser radar according to claim 2, characterized in that the mirror center and the midpoints of four sides of the mirror of the laser mirror (101) are control points for restricting the spatial rotation orientation of the mirror; four linear moving sliding blocks (118) are connected through the ball universal bearing (103); rolling bearings are mounted at two ends of the four linear motion sliding blocks (118) and can respectively move up and down along the track grooves of the four motor supports (104); the x-axis screw rod stepping motor (108) and the y-axis screw rod stepping motor (109) are respectively installed in two motor supports (104) which are connected in the positive direction of the x axis and the y axis, two linear moving sliders (118) are respectively installed on screw rods of the x-axis screw rod stepping motor (108) and the y-axis screw rod stepping motor (109) through gap elimination screw nuts (119), the linear moving sliders (118) are driven by the screw rods of the two stepping motors to do vertical linear motion, and the laser reflector (101) is driven to rotate around the x axis and the y axis; the other two motor brackets (104) are provided with the balancing weights (117) for meeting the static balance and the dynamic balance when the laser reflector (101) rotates around three axes; the lower stepped shaft of the central upright post (107) passes through the miniature ball bearing (111) and is connected with the z-axis stepping motor (112) through a coupler; the four motor supports (104) are respectively and fixedly connected with the four longitudinal deflection hinges (116), so that the four motor supports (104) can slightly deflect along the direction perpendicular to the corresponding edge of the laser reflector (101); meanwhile, the four longitudinal deflection hinges (116) are respectively connected with the four axial deflection hinges (110), so that the four motor supports (104) can slightly deflect along the direction parallel to the corresponding edge of the connected laser mirror (101).

4. The laser scanning attitude angle stabilizing method of the helicopter-borne laser radar as claimed in claim 2, characterized in that the self structural characteristics of the laser scanning attitude angle stabilizing device (1) can meet the requirements of installing the laser reflector (101) with larger size and keeping smaller device volume and mass; the specific size of the adopted laser reflector (101) is 100mm multiplied by 2mm; the laser reflector (101) is arranged on the cross-shaped mirror support rod (102), and four rod ends of the cross-shaped mirror support rod (102) are square joints with threaded holes and can be connected with a screw rod end of the ball head universal bearing (103); the threaded hole end of the ball head universal bearing (103) is connected with the screw end of the linear motion sliding block (118), the linear motion sliding block (118) is fixedly connected with the anti-backlash screw nut (119) and driven by a screw stepping motor to move up and down; the cross-shaped mirror surface supporting rod (102) is fixedly connected with the slotted stainless steel small hemispheroid (105); the slotted stainless steel small hemisphere (105) is a small half steel ball part which is cut by a solid steel ball with the diameter of 30mm at a position 2mm away from the center of the sphere, and a cross-shaped groove with the same size as the center of the cross-shaped mirror surface supporting rod (102) is processed on a cutting plane, so that the cross-shaped mirror surface supporting rod (102) can be firmly embedded into the center of the slotted stainless steel small hemisphere (105); the laser reflector (101) is adhered to the cross-shaped mirror surface supporting rod (102), so that the rotating center of the laser reflector (101) is ensured to be coincided with the spherical center of the slotted stainless steel small hemispheroid (105); the magnetic steel concave spherical body (106) made of a magnetic steel material is fixedly connected with the central upright post (107); the slotted stainless steel small hemispheroid (105) and the magnetic steel concave spherical body (106) are tightly absorbed by magnetic field force, the contact surfaces of the slotted stainless steel small hemispheroid and the magnetic steel concave spherical body are polished to mirror surface precision and coated with lubricating oil, relative displacement cannot occur in a three-dimensional space, and only spherical sliding contact is formed; through the magnetic attraction effect, the slotted stainless steel small hemispheroid (105) and the magnetic steel concave spherical surface (106) can be combined into a magnetic universal ball bearing structure; the thickness of the laser reflector (101) is 2mm, and is exactly equal to the distance of the tangent plane of the slotted stainless steel small hemisphere (105) deviating from the spherical point, so that after the laser reflector (101) is adhered to the cross-shaped mirror surface supporting rod (102), the laser reflection center point of the laser reflector (101) is superposed with the spherical center of the slotted stainless steel small hemisphere (105), and the rotation center of the laser reflector (101) is fixed when rotating; the laser pulse is reflected at the rotation center of the laser reflector (101), and the scanning center point of the emitted laser pulse beam is kept unchanged.

5. The method for stabilizing the laser scanning attitude angle of the helicopter-borne laser radar according to claim 2, wherein optical axes vertically extend from two side surfaces of the linear motion slider (118), the optical axes are fixedly connected with an inner ring of a micro bearing, an outer ring of the micro bearing is placed in a track groove on the side surface of the motor bracket (104), the linear motion slider (118) can be eliminated from rotating along with the radial direction of the screw rod under the action of frictional resistance by virtue of the constraint of the track groove, so that the linear motion slider can only linearly move along the axial direction of the screw rod, and the micro bearing is in rolling contact with the track groove wall, so that the frictional resistance of the track groove to the linear motion slider (118) is reduced; the axial deflection hinge (110) has a certain damping and spring restoring force, and when the laser mirror (101) is perpendicular to the central upright post (107), the motor bracket (104) and the central upright post can be maintained to be parallel; and when the screw rod stepping motor pushes the laser mirror to rotate, the motor bracket (104) generates micro deflection in the rotating directions of the longitudinal deflection hinge (116) and the axial deflection hinge (110) according to the geometrical structure constraint of the laser scanning attitude angle stabilizing device (1).

6. The method for stabilizing laser scanning attitude angle of helicopter laser radar as claimed in claim 2, characterized in that said laser mirror (101) is first rotated by an angle around x-axis

Then rotated about the y-axis

If the linear moving slide block (118) on the x-axis lead screw stepping motor (109) moves by Δ x and the linear moving slide block (118) on the y-axis lead screw stepping motor (109) moves by Δ y, the corresponding relation between the moving distance of the linear moving slide blocks (118) on the two lead screws and the two rotating angles of the laser reflector (101) can be established; the point o is the symmetry center of the laser reflector (101), px ₁ Is the rotation center of the ball head universal bearing (103) on the x axis, px ₂ Is the center point of rotation, px, of said longitudinal yaw hinge (116) on the x-axis ₃ Is the movement central point of the linear motion slide block (118) on the x axis; let py ₁ Is the rotation center point py of the ball head universal bearing (103) on the y axis ₂ Is the center point of rotation of said longitudinal yaw hinge (116) on the y-axis, py ₃ Is the motion central point of the linear motion slide block (118) on the y axis; the rotation process of the laser mirror (101) around two axesOf (5, py) ₁ And py ₃ The line being always parallel to the y-axis, py ₁ And py ₃ Is always perpendicular to py ₂ And py ₃ Connection of (2), at this time, py ₂ And py ₃ Wire winding point py ₂ There is a slight rotation in a direction parallel to the y-axis and a slight rotation in a direction parallel to the x-axis; and for the x-axis, px ₂ And px ₃ Wire winding point px ₂ Only slight rotation in a direction parallel to the x-axis and no slight rotation in a direction parallel to the y-axis; the rotation of the laser reflector (101) around the z axis is relatively independent, and the coupling effect of the laser reflector (101) on the rotation around the x axis and the y axis can be avoided only by controlling the rotation of the z-axis stepping motor.

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