Unmanned vehicle speed constraint method based on road curvature in unstructured environment

Abstract

The invention belongs to the technical field of ground unmanned platform automatic driving, and particularly relates to an unmanned vehicle speed constraint method based on road curvature in an unstructured environment, and the method comprises the steps: carrying out the calculation of the forward path curvature of an unmanned vehicle through the maneuvering global path points of an unmanned platform; and calculating the maximum passing speed which can be borne when passing through the road section by combining a rollover critical value, namely the maximum transverse acceleration, given by a vehicle kinematics model, so as to ensure the maneuvering safety of the unmanned vehicle. In an off-road environment with irregular constraints and scarce and changeable features, the curvature of a driving road is monitored in real time through a global maneuvering path received in the maneuvering process of the unmanned vehicle, the highest maneuvering speed for ensuring safe passing of the vehicle is calculated in real time according to the road curvature, and the safety and high efficiency of maneuvering of the unmanned vehicle can be considered at the same time. Meanwhile, the method is realized only by means of software functions, has good adaptability to various military unmanned platforms, and can effectively control the cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of automatic driving of ground unmanned platforms, and in particular relates to a speed constraint method for unmanned vehicles based on road curvature in an unstructured environment. Background Art

[0002] With the advancement of science and technology, autonomous driving technology has gradually been widely used. In the process of the continuous development of autonomous driving technology, the driving safety factor that people are most concerned about has also become the key to measuring the maturity of autonomous driving technology. Common technologies include active braking, active avoidance, automatic body stability system, etc. In addition, it also includes the most basic speed constraint. Too fast maneuvering speed can easily cause the risk of loss of control during the vehicle's autonomous driving process, but too slow maneuvering speed makes the experience and practicality of autonomous driving technology poor. Therefore, it is very important to study how to perform efficient autonomous driving while ensuring the safety of vehicle driving.

[0003] In the field of civilian autonomous driving, this problem is relatively simple. The field of civilian autonomous driving mainly targets urban structured environments, which have many characteristics and have formed unified traffic rules. Vehicles can use a variety of means to restrict speed, such as slowing down at traffic lights, slowing down at crosswalks, and controlling vehicle speed according to speed limit signs.

[0004] However, in the field of military autonomous driving, it is more oriented towards unstructured environments under off-road conditions, whose typical characteristics are inconsistent environmental features, lack of traffic rules, and complex road environment. Therefore, it is difficult to form a highly adaptable unmanned vehicle speed constraint method through traditional perception.

[0005] Existing speed constraint methods mainly rely on speed limits under urban traffic regulations. The vehicle's own maneuvering speed is not restricted, and it relies more on the driver to coordinate the accelerator and brake to achieve speed control. This also leads to some deficiencies in the actual application of autonomous driving technology in civilian environments in off-road environments, especially in complex terrain environments such as mountains, forests, and deserts. It is difficult for autonomous driving to obtain effective speed constraints, which usually manifests as too fast speed, insufficient vehicle maneuvering safety, or too slow speed, low efficiency of autonomous driving. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] The technical problem to be solved by the present invention is: how to provide a speed restriction method for an unmanned vehicle.

[0008] (II) Technical solution

[0009] In order to solve the above technical problems, the present invention provides a speed constraint method for an unmanned vehicle based on road curvature in an unstructured environment. The method calculates the forward path curvature of the unmanned vehicle through the global path points of the unmanned platform maneuvering, and combines the rollover critical value given by the vehicle kinematic model, that is, the maximum lateral acceleration, to calculate the maximum travel speed that can be tolerated when passing through the road section, thereby ensuring the safety of the unmanned vehicle maneuvering.

[0010] Among them, in the unmanned vehicle speed constraint method, the unmanned vehicle maneuvers in the off-road environment through the global path point to guide the unmanned vehicle to perform autonomous maneuvers. The global path point refers to a plurality of latitude and longitude coordinate points arranged in sequence, which are connected in sequence to form a continuous driving path. The interval between two longitude and latitude coordinate points is set to a certain number of meters;

[0011] The geodetic coordinate system used in the method is the CGCS2000 coordinate system. The latitude and longitude coordinates are transformed by the ellipsoid Gaussian projection method to finally obtain the metric unit result. The calculation method is as shown in formula (1):

[0012]

[0013] The calculation of n, t, c, A, and M is shown in (2):

[0014]

[0015] e2 is given by e2=1-(1-f) 2 ×(sin(Lat)) 2 The calculation shows that (Lon, Lat) is the longitude and latitude information under GPS / Beidou positioning, (x, y) is the position in the converted CGCS2000 coordinate system, in meters; a is the semi-major axis of the earth; f is the flattening of the earth; lon0 is the central meridian of the earth; k0 is the scale factor, which is taken as 1 during the calculation process;

[0016] The global path is represented by the converted coordinates; the coordinates of the first point p1 are (x1, y1), the coordinates of the second point p2 are (x2, y2), and the coordinates of the third point p3 are (x3, y3); the line segment between p1 and p2 is recorded as road_line_1, and the line segment between p2 and p3 is recorded as road_line_2;

[0017] The angles γ1 and γ2 between road_line_1 and road_line_2 and the east direction are calculated by formula (3):

[0018]

[0019] Based on γ1 and γ2, the angle θ1 between road_line_1 and road_line_2 is calculated using formula (4):

[0020] θ1=γ2-γ1 (4)

[0021] In off-road environments, unmanned vehicles need to ensure that they maintain the maximum allowed speed within the range of the curve to ensure maneuverability and safety; therefore, the vehicle speed needs to be reduced to the allowed range when entering a curve; at the same time, in order to improve the adaptability of the method, a road threshold of several meters is set to solve the road curvature, and 5 road_lines are selected as a group to iteratively solve the road curvature, that is, the 1st to 5th road_lines are solved once, and the 2nd to 6th road_lines are solved once, and then calculated in sequence to ensure that the global path can be completely traversed;

[0022] The sum of the angles of the five road_line segments is taken as the steering angle of the road segment, as shown in formula (5):

[0023]

[0024] The five road sections are fitted with arcs with an arc length of 50 meters. The turning radius r is calculated using formula (6), and the maximum lateral acceleration a1 provided by the vehicle kinematic model is used to solve the maximum vehicle speed v allowed on the current road section using formula (7): max :

[0025]

[0026] In the method, the interval between two longitude and latitude coordinate points is set to 10 meters.

[0027] In the method, a road threshold of 50 meters in length is set.

[0028] (III) Beneficial effects

[0029] The present invention provides a method for constraining the speed of unmanned vehicles based on road curvature in an unstructured environment. In an off-road environment with no rule constraints and scarce and variable features, the curvature of the driving road is monitored in real time through the global maneuvering path received during the maneuvering process of the unmanned vehicle, and the maximum maneuvering speed to ensure the safe passage of the vehicle is calculated in real time according to the road curvature, which can take into account both the safety and efficiency of the maneuvering of the unmanned vehicle. At the same time, the method itself is only implemented by software functions, has good adaptability to various military unmanned platforms, and can effectively control costs.

[0030] Compared with the prior art, the present invention includes the following innovations:

[0031] 1. The global path information received by the unmanned vehicle during autonomous maneuvering is combined with the vehicle's own kinematic model to automatically generate a road speed constraint method to ensure that the vehicle can maneuver at the highest speed while ensuring safety.

[0032] 2. The longitude and latitude are converted into the CGCS2000 geodetic coordinate system through the Gaussian projection method of the ellipsoid. In this coordinate system, the line segments formed by the global path points within a range of 50 meters are fitted by arcs, the turning angle is obtained, and the turning radius is calculated.

[0033] 3. Solve the segmented road curvature of the entire path through a step-by-step iterative method to ensure that the path is fully traversed and applicable.

[0034] 4. The maximum lateral acceleration threshold given by a simple vehicle kinematics model can be combined with the required road curvature to obtain the maximum vehicle speed of the corresponding section.

[0035] The beneficial effects of the present invention include:

[0036] 1. The present invention calculates the road curvature through the global path, combines the kinematic model of the unmanned vehicle to solve the maximum safe speed allowed by the road in a piecewise manner, controls the unmanned vehicle to perform autonomous maneuvers, and improves the driving safety of military unmanned vehicles only through software algorithms, which is conducive to the large-scale promotion and use in the field of military unmanned vehicles and can effectively control costs;

[0037] 2. The present invention solves the problem of how to constrain the speed of unmanned vehicles in off-road environments that lack environmental features and driving rules. The proposed method can adaptively control the speed of unmanned vehicles, has strong universality, and can basically cover most situations of autonomous maneuvers of unmanned vehicles in off-road environments;

[0038] 3. The present invention does not rely on traffic rules and good road environment perception assistance. It can control the speed of the unmanned vehicle only through the global path required for the unmanned vehicle to maneuver in an off-road environment, which not only ensures the safety of the unmanned vehicle's autonomous maneuvering, but also ensures the efficiency of the unmanned vehicle's autonomous maneuvering. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flow chart of the technical solution of the present invention.

[0040] Figure 2 Schematic diagram of the global path of the unmanned vehicle.

[0041] Figure 3 Schematic diagram for solving the angle of segmented roads.

[0042] Figure 4 Schematic diagram for solving the maximum speed on a segmented road. DETAILED DESCRIPTION

[0043] In order to make the purpose, content, and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the accompanying drawings and examples.

[0044] In order to solve the above technical problems, the present invention provides a speed constraint method for an unmanned vehicle based on road curvature in an unstructured environment. The method calculates the forward path curvature of the unmanned vehicle through the global path points of the unmanned platform maneuvering, and combines the rollover critical value given by the vehicle kinematic model, that is, the maximum lateral acceleration, to calculate the maximum travel speed that can be tolerated when passing through the road section, thereby ensuring the safety of the unmanned vehicle maneuvering.

[0045] In the unmanned vehicle speed constraint method, the unmanned vehicle maneuvers in the off-road environment through the global path point to guide the unmanned vehicle to perform autonomous maneuvers. The global path point refers to a plurality of latitude and longitude coordinate points arranged in sequence, which are connected in sequence to form a continuous driving path. The interval between two longitude and latitude coordinate points is set to 10 meters. Figure 2 As shown;

[0046] The geodetic coordinate system used in the method is the CGCS2000 (China Geodetic Coordinate System 2000) coordinate system. The longitude and latitude coordinates are transformed by the ellipsoid Gaussian projection method, and finally the meter (m) unit result is obtained. The calculation method is as shown in formula (1):

[0047]

[0048] The calculation of n, t, c, A, and M is shown in (2):

[0049]

[0050] e2 is given by e2=1-(1-f) 2 ×(sin(Lat)) 2 The calculation shows that (Lon, Lat) is the longitude and latitude information under GPS / Beidou positioning, (x, y) is the position in the converted CGCS2000 coordinate system, in meters; a is the semi-major axis of the earth; f is the flattening of the earth; lon0 is the central meridian of the earth; k0 is the scale factor, which is taken as 1 during the calculation process;

[0051] The global path is represented by the transformed coordinates, such as Figure 3 As shown; the coordinates of the first point p1 are (x1, y1), the coordinates of the second point p2 are (x2, y2), and the coordinates of the third point p3 are (x3, y3); the line segment between p1 and p2 is recorded as road_line_1, and the line segment between p2 and p3 is recorded as road_line_2;

[0052] The angles γ1 and γ2 between road_line_1 and road_line_2 and the east direction are calculated by formula (3):

[0053]

[0054] Based on γ1 and γ2, the angle θ1 between road_line_1 and road_line_2 is calculated using formula (4):

[0055] θ1=γ2-γ1 (4)

[0056] According to engineering test experience, in off-road environments, unmanned vehicles need to ensure that they maintain the maximum allowable speed within the range of the curve to ensure maneuverability and safety; therefore, the vehicle speed needs to be reduced to the allowable range when entering a curve; at the same time, in order to improve the adaptability of the method, a 50-meter road threshold is set to solve the road curvature, and 5 road_lines are selected as a group to iteratively solve the road curvature, that is, the 1st to 5th road_lines are solved once, and the 2nd to 6th road_lines are solved once, and then calculated in sequence to ensure that the global path can be completely traversed;

[0057] The sum of the angles of the five road_line segments is taken as the steering angle of the road segment, as shown in formula (5):

[0058]

[0059] like Figure 4 As shown in the figure, the five road sections are fitted with circular arcs. The arc length is taken as an approximate value, which is about 50 meters. The turning radius r is calculated by formula (6), and the maximum lateral acceleration a1 provided by the vehicle kinematic model is used to solve the maximum vehicle speed v allowed by the current road section by formula (7):

[0060] max :

[0061]

[0062] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A speed constraint method for unmanned vehicles based on road curvature in an unstructured environment, characterized in that: The method calculates the forward path curvature of the unmanned vehicle through the global path points of the unmanned platform maneuvering, and combines the rollover critical value given by the vehicle kinematic model, that is, the maximum lateral acceleration, to calculate the maximum travel speed that can be tolerated when passing through the road section, thereby ensuring the safety of the unmanned vehicle maneuvering.

2. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: In the unmanned vehicle speed constraint method, the unmanned vehicle maneuvers in the off-road environment through the global path point to guide the unmanned vehicle to perform autonomous maneuvers. The global path point refers to a plurality of latitude and longitude coordinate points arranged in sequence, which are connected in sequence to form a continuous driving path. The interval between two longitude and latitude coordinate points is set to a certain number of meters. The geodetic coordinate system used in the method is the CGCS2000 coordinate system. The latitude and longitude coordinates are transformed by the ellipsoid Gaussian projection method to finally obtain the metric unit result. The calculation method is as shown in formula (1): The calculation of n, t, c, A, and M is shown in (2): e2 is given by e2=1-(1-f) 2 ×(sin(Lat)) 2 The calculation shows that (Lon, Lat) is the longitude and latitude information under GPS / Beidou positioning, (x, y) is the position in the converted CGCS2000 coordinate system, in meters; a is the semi-major axis of the earth; f is the flattening of the earth; lon0 is the central meridian of the earth; k0 is the scale factor, which is taken as 1 during the calculation process; The global path is represented by the converted coordinates; the coordinates of the first point p1 are (x1, y1), the coordinates of the second point p2 are (x2, y2), and the coordinates of the third point p3 are (x3, y3); the line segment between p1 and p2 is recorded as road_line_1, and the line segment between p2 and p3 is recorded as road_line_2; The angles γ1 and γ2 between road_line_1 and road_line_2 and the east direction are calculated by formula (3): Based on γ1 and γ2, the angle θ1 between road_line_1 and road_line_2 is calculated using formula (4): θ1=γ2-γ1 (4) In off-road environments, unmanned vehicles need to ensure that they maintain the maximum allowed speed within the range of the curve to ensure maneuverability and safety; therefore, the vehicle speed needs to be reduced to the allowed range when entering a curve; at the same time, in order to improve the adaptability of the method, a road threshold of several meters is set to solve the road curvature, and 5 road_lines are selected as a group to iteratively solve the road curvature, that is, the 1st to 5th road_lines are solved once, and the 2nd to 6th road_lines are solved once, and then calculated in sequence to ensure that the global path can be completely traversed; The sum of the angles of the five road_line segments is taken as the steering angle of the road segment, as shown in formula (5): The five road sections are fitted with arcs with an arc length of 50 meters. The turning radius r is calculated using formula (6), and the maximum lateral acceleration a1 provided by the vehicle kinematic model is used to solve the maximum vehicle speed v allowed on the current road section using formula (7): max :

3. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 2, characterized in that: In the method, the interval between two longitude and latitude coordinate points is set to 10 meters; In the method, a road threshold of 50 meters in length is set.

4. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: The geodetic coordinate system adopted by the method is the CGCS2000 coordinate system.

5. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: (Lon, Lat) is the longitude and latitude information under GPS / Beidou positioning.

6. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: (x, y) is the position in the converted CGCS2000 coordinate system, in meters.

7. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: a is the semi-major axis of the Earth.

8. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: f is the flattening of the Earth.

9. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: lon0 is the central meridian of the earth.

10. The unmanned vehicle speed constraint method based on road curvature in an unstructured environment as claimed in claim 1, characterized in that: k0 is the proportional factor, which is taken as 1 during the calculation process.

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