A method and device for distinguishing laser point cloud distortion of celestial body exploration vehicle

Abstract

The present invention relates to a method and device for distinguishing the distortion of laser point cloud of a celestial body exploration vehicle, the method comprising: obtaining the vertical vibration speed v of the celestial body exploration vehicle within the laser radar scanning cycle; if the vertical vibration speed v>Threshold, the laser point cloud is distorted, otherwise the laser point cloud is not distorted, wherein Threshold is the vertical vibration speed threshold. Compared with the prior art, the present invention can accurately judge the distortion of the laser point cloud, avoid accidents caused by the distortion of the self-vehicle positioning and the target identification positioning, and improve the safety of intelligent driving on the celestial body and the ground surface.

Description

Technical Field

[0001] The present invention relates to the field of celestial body and earth surface intelligent driving technology, and in particular to a method and device for distinguishing laser point cloud distortion of a celestial body exploration vehicle. Background Art

[0002] An autonomous vehicle probe vehicle is a prerequisite for celestial body detection. Accurate probe vehicle location information and target distance measurement are crucial for autonomous driving. Stable high-precision positioning information under all working conditions is a necessary condition to ensure path planning and precise chassis control. The accuracy of the GNSS / GPS positioning system usually used in vehicle terminals is about a few meters, and it cannot be applied to places where celestial surface signals are missing; and visual sensors are also subject to defects such as light, weather, and nighttime; in comparison, LiDAR has the advantages of strong anti-interference ability, high detection accuracy, and long detection distance. Therefore, LiDAR is the most relied upon high-precision positioning sensor for achieving high-precision positioning in the field of autonomous driving.

[0003] However, there are many rough roads on the surface of celestial bodies. During the scanning process of the laser radar, the laser radar starts scanning from the initial position (0°) and performs 360° scanning and ranging. At the same time, multiple beams are scanned in the vertical direction. The laser points in the laser radar are collected at different times. In the case of bumpy driving, the vibration displacement and scanning distance error of the laser radar cause point cloud distortion. Therefore, the research and evaluation of laser radar point cloud distortion is very important for obtaining the real environment.

[0004] At present, the existing autonomous driving lidar perception systems are mostly used in stable driving conditions. They lack the ability to judge the distortion of the environment perception when the exploration vehicle is driving bumpy, which to a certain extent poses a safety hazard to the autonomous driving of the celestial exploration vehicle. In addition, the distortion of the lidar point cloud leads to the distortion of the vehicle positioning and target recognition positioning, which in turn leads to accidents. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and to provide a method and device for distinguishing the distortion of laser point cloud of celestial body exploration vehicle.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for distinguishing distortion of laser point cloud of a celestial body exploration vehicle, the method comprising:

[0008] Obtain the vertical vibration velocity v of the celestial body exploration vehicle during the laser radar scanning cycle;

[0009] If the vertical vibration velocity v>Threshold, the laser point cloud is distorted, otherwise the laser point cloud is not distorted, where Threshold is the vertical vibration velocity threshold.

[0010] Preferably, the method also includes: synchronously acquiring the vertical tilt angle θ of the celestial exploration rover when acquiring the vertical vibration velocity v of the celestial exploration rover. In the case that the laser point cloud is distorted, if the vertical tilt angle θ of the celestial exploration rover is 0, the laser point cloud only has vertical distortion; if the vertical tilt angle θ of the celestial exploration rover is not 0, the laser point cloud has both vertical distortion and tilt distortion.

[0011] Preferably, when the laser point cloud only has vertical distortion, the distortion amount of the laser point cloud distance measurement is:

[0012] L2-L1=-S·cotβ,

[0013] Among them, L2 is the laser point cloud measurement distance when only vertical distortion exists, L1 is the actual measurement point distance, and β is the inclination angle of the measurement surface.

[0014] Preferably, when the laser point cloud has both vertical distortion and tilt distortion, the distortion amount of the laser point cloud distance measurement is:

[0015]

[0016] L3 is the laser point cloud measurement distance when both vertical distortion and tilt distortion exist, L1 is the actual measurement point distance, β is the tilt angle of the measurement surface, and S is the vertical vibration displacement of the celestial exploration vehicle.

[0017] Preferably, the vertical vibration velocity of the celestial exploration vehicle is obtained in the following manner: first, the time-domain vertical vibration acceleration of the celestial exploration vehicle within the laser radar scanning period is obtained, and then the time-domain vertical vibration acceleration is discrete Fourier transformed to obtain the frequency vertical vibration acceleration, and finally, the frequency vertical vibration acceleration is integrated to obtain the vertical vibration velocity.

[0018] Preferably, the vertical vibration displacement of the celestial exploration vehicle is obtained in the following manner: first, the time domain vertical vibration acceleration of the celestial exploration vehicle within the laser radar scanning period is obtained, and then the time domain vertical vibration acceleration is discrete Fourier transformed to obtain the frequency vertical vibration acceleration, then, the frequency vertical vibration acceleration is integrated to obtain the vertical vibration velocity, and finally, the vertical vibration velocity is integrated to obtain the vertical vibration displacement.

[0019] Preferably, the vertical vibration velocity threshold Threshold is: Threshold=Φ·f, wherein f is the rotation frequency of the laser radar, Φ is the frequency factor, and Φ is a constant.

[0020] Preferably, the time-domain vertical vibration acceleration is obtained by an inertial measurement unit installed on a celestial exploration rover.

[0021] Preferably, the vertical tilt angle of the celestial exploration rover is also obtained by an inertial measurement unit installed on the celestial exploration rover.

[0022] A celestial body exploration vehicle laser point cloud distortion discrimination device comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor is used to implement the celestial body exploration vehicle laser point cloud distortion discrimination method when executing the computer program.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention determines the distortion of the laser radar's perception of the environment based on the vertical vibration velocity of the celestial body exploration vehicle, and the determination is simple and accurate;

[0025] (2) Based on the distortion discrimination of laser point cloud, the present invention can quantitatively calculate the distortion amount, so as to correct the measurement value of laser radar, avoid accidents caused by distortion of vehicle positioning and target identification positioning, and improve the safety of intelligent driving on celestial bodies and surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of a method for distinguishing laser point cloud distortion of a celestial body exploration vehicle according to the present invention;

[0027] Figure 2 It is a schematic diagram of the structure of the motion mechanism and distributed sensing device of the celestial body exploration vehicle of the present invention;

[0028] Figure 3 Schematic diagram of vertical and horizontal scanning beams of the laser radar;

[0029] Figure 4 It is the registration model of the lidar points during the entire lidar scanning process;

[0030] Figure 5 Schematic diagram of laser beam scanning results in the embodiment.

[0031] Figure 2 In the figure, 1 is the walking wheel, 2 is the robotic arm, 3 is the lidar, 4 is the camera, and 5 is the inertial measurement unit. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Note that the following embodiments are merely illustrative in nature, and the present invention is not intended to limit its applicable objects or uses, and the present invention is not limited to the following embodiments.

[0033] Example

[0034] The vibration of the laser radar is easily affected by factors such as road roughness and vehicle speed, and the vibration displacement of the laser radar is difficult to estimate. The present invention designs a detection device for the laser point cloud distortion of the celestial body exploration vehicle, obtains the time domain vibration displacement through the frequency domain acceleration integration method, and performs distortion prediction and scanning distance output for the laser point cloud. The present invention provides an important discrimination method for the vibration distortion of the laser radar point cloud.

[0035] like Figure 1 As shown, this embodiment provides a method for distinguishing distortion of laser point cloud of a celestial body exploration vehicle, the method comprising:

[0036] Obtain the vertical vibration velocity v of the celestial body exploration vehicle during the laser radar scanning cycle;

[0037] If the vertical vibration velocity v>Threshold, the laser point cloud is distorted, otherwise the laser point cloud is not distorted, where Threshold is the vertical vibration velocity threshold, and the vertical vibration velocity threshold Threshold is: Threshold=Φ·f, where f is the rotation frequency of the laser radar, Φ is the frequency factor, and Φ is a constant.

[0038] The method also includes: when obtaining the vertical vibration speed v of the celestial exploration vehicle, synchronously obtaining the vertical tilt angle θ of the celestial exploration vehicle. When the laser point cloud is distorted, if the vertical tilt angle θ of the celestial exploration vehicle is 0, the laser point cloud only has vertical distortion. If the vertical tilt angle θ of the celestial exploration vehicle is not 0, the laser point cloud has both vertical distortion and tilt distortion.

[0039] When the laser point cloud only has vertical distortion, the distortion of the laser point cloud distance measurement is:

[0040] L2-L1=-S·cotβ,

[0041] Among them, L2 is the laser point cloud measurement distance when only vertical distortion exists, L1 is the actual measurement point distance, and β is the inclination angle of the measurement surface.

[0042] When the laser point cloud has both vertical distortion and tilt distortion, the distortion of the laser point cloud distance measurement is:

[0043]

[0044] L3 is the laser point cloud measurement distance when both vertical distortion and tilt distortion exist, L1 is the actual measurement point distance, β is the tilt angle of the measurement surface, and S is the vertical vibration displacement of the celestial exploration vehicle.

[0045] The vertical vibration velocity of the celestial exploration rover is obtained in the following way: first, the time-domain vertical vibration acceleration of the celestial exploration rover during the laser radar scanning period is obtained, then the time-domain vertical vibration acceleration is discrete Fourier transformed to obtain the frequency vertical vibration acceleration, and finally, the frequency vertical vibration acceleration is integrated to obtain the vertical vibration velocity.

[0046] The vertical vibration displacement of the celestial exploration rover is obtained in the following way: first, the time-domain vertical vibration acceleration of the celestial exploration rover during the laser radar scanning period is obtained, and then the time-domain vertical vibration acceleration is discrete Fourier transformed to obtain the frequency vertical vibration acceleration, then the frequency vertical vibration acceleration is integrated to obtain the vertical vibration velocity, and finally, the vertical vibration velocity is integrated to obtain the vertical vibration displacement. The time-domain vertical vibration acceleration is obtained by the inertial measurement unit installed on the celestial exploration rover, and the vertical tilt angle of the celestial exploration rover is also obtained by the inertial measurement unit installed on the celestial exploration rover.

[0047] Based on the above, the present invention mainly includes the following contents:

[0048] (1) Input device for astronomical rover laser point cloud distortion measurement

[0049] The body exploration vehicle usually includes a wheeled walking device and a manipulator, such as Figure 2 As shown in (a), it includes a walking wheel 1 and a mechanical arm 2, and the vehicle body sensor device includes a laser radar 3, a camera 4 and an inertial measurement unit 5. Figure 2 As shown in (b).

[0050] The laser radar achieves 360° rotation scanning through the motor shaft to obtain environmental distance information. According to the number of scanning lines in the vertical direction of the laser radar, the types of laser radar can be divided into 64 lines, 32 lines, 16 lines, 8 lines, 4 lines and 1 line, such as Figure 3 As shown, Figure 3 (a) is a schematic diagram of the vertical scanning beam of the laser radar. Figure 3 (b) is a schematic diagram of the horizontal scanning beam of the laser radar. By controlling the rotation speed of the laser radar motor shaft, a rotation frequency of 10-20Hz can be achieved.

[0051] There are some potholes and meteorites on the surface of the earth. The rocks and sand on the damaged road further aggravate the vibration of the rover. The uneven road surface transmits vibrations through the tires and suspension, resulting in vertical scanning registration errors of the lidar. At the same time, the lidar cannot complete the synchronous scanning registration of the wire harness at the initial moment of a single frame, which poses a great challenge to the lidar in obtaining real environmental distance information during bumpy driving. Figure 4 The registration model of the lidar points during the entire lidar scan is shown. Therefore, during bumpy driving, all points in the frame are not registered synchronously at the same height.

[0052] In order to distinguish and measure the distortion of laser point cloud, an IMU inertial sensor is installed on the celestial exploration vehicle. The IMU sensor outputs vibration acceleration, which is used to measure the output vibration acceleration. Figure 3 (or Figure 4 ) to realize the motion prediction of point cloud registration distortion. The input device of the laser point cloud distortion measurement only detects the vertical displacement change, and the resolution of the horizontal rotation angle remains unchanged.

[0053] (2) Displacement calculation process based on time-frequency domain transformation and vibration acceleration integration

[0054] The position of the laser radar scanning point is the superposition of the laser radar axis rotation and vibration displacement. The vibration of the probe car caused by the uneven road surface is random, and the mass, stiffness and damping coefficient of the exciting force transmission chain are difficult to measure. Therefore, the velocity and displacement can be obtained by integrating the vibration acceleration. However, due to the unknown initial conditions, there are still many difficulties in integrating the time domain acceleration. In order to improve the accuracy of the vibration acceleration integration, the frequency integration method is used to calculate the vibration displacement.

[0055] The time domain vibration acceleration (a(r)) is subjected to discrete Fourier transform (DFT), and then the frequency signal in equation (1) is obtained, where N represents the number of sampled data.

[0056]

[0057] The vibration velocity is obtained by integrating the frequency domain acceleration signal, as shown in equation (2).

[0058]

[0059] The vertical vibration displacement is obtained by integrating the frequency domain vibration velocity, as shown in equation (3). In equations (2) and (3), the definition of H(k) is shown in equation (4).

[0060]

[0061]

[0062] In the formula, f d Indicates the lower limit of the cut-off frequency, f u represents the upper limit of the cutoff frequency, and Δf represents the frequency resolution. After that, the vibration velocity and displacement in the time domain can be obtained by performing inverse Fourier transform on equations (2) and (3).

[0063] The degree of distortion of the point cloud is determined according to the change in the vertical height displacement of the laser radar scanning point: when the vertical vibration velocity v>Threshold, the laser point cloud is distorted, otherwise the laser point cloud is not distorted, where Threshold is the vertical vibration velocity threshold, and the vertical vibration velocity threshold Threshold is: Threshold=Φ·f, where f is the rotation frequency of the laser radar, Φ is the frequency factor, Φ is a constant, 10HZ<f<20HZ.

[0064] The laser radar scans the surrounding environment to sense the distance and thus construct a three-dimensional environment. The point cloud distortion results mainly include vertical distortion and tilt distortion, such as Figure 5 The laser beam scanning results are shown in Figure 2. The output distance of the vertical vibration loss is shown in formula (5), and the output distance of the tilt loss is shown in formula (6).

[0065] Output distance of vertical distortion:

[0066] L2=L1-S·cotβ (5)

[0067] Output distance of tilt distortion:

[0068]

[0069] Furthermore, when the laser point cloud only has vertical distortion, the distortion of the laser point cloud distance measurement is:

[0070] L2-L1=-S·cotβ (7)

[0071] Where L2 is the laser point cloud measurement distance when only vertical distortion exists, L1 is the actual measurement point distance, and β is the inclination angle of the measurement surface. Formula (7) is obtained from formula (5).

[0072] When the laser point cloud has both vertical distortion and tilt distortion, the distortion of the laser point cloud distance measurement is:

[0073]

[0074] L3 is the laser point cloud measurement distance when both vertical distortion and tilt distortion exist, L1 is the actual measurement point distance, β is the tilt angle of the measurement surface, S is the vertical vibration displacement of the celestial exploration vehicle, and formula (8) is obtained from formula (6).

[0075] The vibration distortion of the laser point cloud of the celestial body exploration vehicle depends on the vibration acceleration and vibration frequency. The vibration velocity is proportional to the vibration acceleration and inversely proportional to the vibration frequency; the vibration displacement is proportional to the vibration velocity and inversely proportional to the vibration frequency.

[0076] Based on the above-mentioned celestial body exploration rover laser point cloud distortion discrimination method, this embodiment also provides a celestial body exploration rover laser point cloud distortion discrimination device, including a memory and a processor, the memory is used to store a computer program, and the processor is used to implement the celestial body exploration rover laser point cloud distortion discrimination method when executing the computer program.

[0077] The above embodiments are merely examples and do not limit the scope of the present invention. These embodiments can also be implemented in various other ways, and various omissions, substitutions, and changes can be made without departing from the technical concept of the present invention.

Claims

1. A method for distinguishing distortion of laser point cloud of celestial body exploration vehicle, characterized in that: The method includes: Obtain the vertical vibration velocity v of the celestial body exploration vehicle during the laser radar scanning cycle; If the vertical vibration velocity v>Threshold, the laser point cloud is distorted, otherwise the laser point cloud is not distorted, where Threshold is the vertical vibration velocity threshold; The method further includes: synchronously acquiring a vertical tilt angle θ of the celestial body exploration vehicle when acquiring a vertical vibration speed v of the celestial body exploration vehicle, and in the case where the laser point cloud is distorted, if the vertical tilt angle θ of the celestial body exploration vehicle is 0, the laser point cloud only has vertical distortion, and if the vertical tilt angle θ of the celestial body exploration vehicle is not 0, the laser point cloud has both vertical distortion and tilt distortion; When the laser point cloud only has vertical distortion, the distortion of the laser point cloud distance measurement is: L2-L1=-S·cotβ, Among them, L2 is the laser point cloud measurement distance when only vertical distortion exists, L1 is the actual measurement point distance, and β is the inclination angle of the measurement surface; When the laser point cloud has both vertical distortion and tilt distortion, the distortion of the laser point cloud distance measurement is: L3 is the laser point cloud measurement distance when both vertical distortion and tilt distortion exist, L1 is the actual measurement point distance, β is the tilt angle of the measurement surface, and S is the vertical vibration displacement of the celestial exploration vehicle.

2. The method for distinguishing laser point cloud distortion of a celestial body exploration vehicle according to claim 1, characterized in that: The vertical vibration velocity of the celestial exploration vehicle is obtained in the following manner: first, the time-domain vertical vibration acceleration of the celestial exploration vehicle within the laser radar scanning period is obtained, and then the time-domain vertical vibration acceleration is discrete Fourier transformed to obtain the frequency vertical vibration acceleration, and finally, the frequency vertical vibration acceleration is integrated to obtain the vertical vibration velocity.

3. The method for distinguishing laser point cloud distortion of a celestial body exploration vehicle according to claim 1, characterized in that: The vertical vibration displacement of the celestial exploration vehicle is obtained in the following manner: first, the time-domain vertical vibration acceleration of the celestial exploration vehicle within the laser radar scanning period is obtained, and then the time-domain vertical vibration acceleration is discrete Fourier transformed to obtain the frequency vertical vibration acceleration, then, the frequency vertical vibration acceleration is integrated to obtain the vertical vibration velocity, and finally, the vertical vibration velocity is integrated to obtain the vertical vibration displacement.

4. The method for distinguishing distortion of laser point cloud of celestial body exploration vehicle according to claim 1, characterized in that: The vertical vibration velocity threshold Threshold is: Threshold=Φ·f, wherein f is the rotation frequency of the laser radar, Φ is the frequency factor, and Φ is a constant.

5. The method for distinguishing laser point cloud distortion of a celestial body exploration vehicle according to claim 2 or 3, characterized in that: The time-domain vertical vibration acceleration is obtained by an inertial measurement unit installed on the celestial exploration vehicle.

6. The method for distinguishing laser point cloud distortion of a celestial body exploration vehicle according to claim 1, characterized in that: The vertical tilt angle of the celestial body exploration vehicle is also obtained by an inertial measurement unit installed on the celestial body exploration vehicle.

7. A laser point cloud distortion discrimination device for a celestial body exploration vehicle, characterized in that: It comprises a memory and a processor, wherein the memory is used to store a computer program, and the processor is used to implement the celestial body exploration vehicle laser point cloud distortion discrimination method as claimed in any one of claims 1 to 4 when executing the computer program.

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