Unmanned surface vehicle based offshore search area coverage path planning method

Abstract

The application discloses a kind of based on unmanned ship's sea search area coverage path planning method, S 1: obtaining sea search area;S2: unmanned ship system model is built;S3: determine search direction, global path planning is carried out to search area;S4: artificial potential field method is adopted to plan local path, constructs repulsive potential field function, sets multiple unmanned ship obstacle avoidance decision subarea, and each unmanned ship obstacle avoidance decision subarea is configured with the corresponding subarea repulsive potential field function of itself;Wherein, the repulsive potential field function can represent the distance relationship between unmanned ship and target point;S5: unmanned ship is navigated according to original planning path in search area and detects target and unknown obstacle: S6: after unmanned ship searches entire search area, end task.The application uses double-layer planning to construct static route;In the process of unmanned ship navigation, multiple obstacle avoidance algorithms are used to construct dynamic route, guarantee the safe navigation of unmanned ship while meeting the requirement of uniform coverage to search area.

Description

Technical Field

[0001] This invention relates to the field of intelligent control technology for unmanned surface vessels (USVs), and in particular to a method for planning a maritime search area coverage path based on USVs. Background Technology

[0002] With the rapid development of the shipping industry and the increasing frequency of maritime transport and trade, maritime emergencies are becoming more frequent and complex, necessitating greater attention to the safety of personnel at sea. Maritime search and rescue is a necessary means to ensure the safety of life and property at sea and create a favorable maritime transportation environment. Search and rescue includes both searching and rescue operations, with searching being the prerequisite and key to all rescue work. However, judging from the current state of maritime search and rescue work, it mainly relies on manual operation of vessels to carry out search tasks. Due to limitations in search facilities and coordination capabilities, it suffers from problems such as long search times, low efficiency, and a high risk of missed or false detections.

[0003] As intelligent vessels with autonomous navigation, control, and communication transmission capabilities, unmanned surface vessels (USVs) possess autonomy, flexibility, intelligence, and information technology. Utilizing USVs for search missions provides a new approach to maritime search and rescue operations. USVs are highly maneuverable, low-cost, and have a wide search range, which can greatly improve search efficiency, expand the search area, and perform search missions day and night in harsh marine environments.

[0004] In practice, when the search environment is fully known, the path planning methods currently available can yield satisfactory results. However, in unknown environments, such as when the number and location of targets or obstacles are unknown, existing path planning methods cannot achieve uniform coverage of the search area, leading to problems such as target omission. Therefore, when planning the search path for unmanned surface vessels at sea, it is necessary to consider how to achieve maximum coverage of the search area in unknown environments. Summary of the Invention

[0005] This invention provides a method for maritime search area coverage path planning based on unmanned surface vessels, in order to overcome the problem that existing path planning methods cannot achieve uniform coverage of the search area in unknown environments, resulting in target omission.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for planning a maritime search area coverage path based on an unmanned surface vessel (USV) comprises the following steps:

[0008] S1: Obtain the search area at sea and read the electronic nautical chart information of the search area;

[0009] S2: Construct an unmanned surface vessel system model based on the ship's coordinate system and the global coordinate system;

[0010] S3: Determine the search direction and perform global path planning for the search area based on parallel line scanning search. Set the interval width between two parallel line paths in the search area, that is, the width of the area scanned when the unmanned surface vessel travels straight along the parallel line path is D.

[0011] S4: Based on the known obstacle information within the search area provided by the electronic nautical chart, when performing local path planning using the artificial potential field method, a repulsive potential field function U is constructed. o (X), multiple unmanned surface vessel (USV) obstacle avoidance decision zones are set, and a corresponding repulsive potential field function is configured for each USV obstacle avoidance decision zone; wherein, the repulsive potential field function U o (X) can characterize the distance relationship between the unmanned surface vessel and the target point d(X, X). g );

[0012] S5: The unmanned surface vessel navigates within the search area according to the original planned path determined by global path planning and local path planning, and detects targets and unknown obstacles through sensors.

[0013] When a target is detected, the target coordinates in the global coordinate system are sent to shore-based or search and rescue vessels, and the vessel continues to navigate along the original planned path to search for the target.

[0014] When an unknown obstacle is detected, the unmanned surface vessel (USV) determines whether there is an obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system. If there is an obstacle avoidance target point, the artificial potential field method is used to plan the path for obstacle avoidance. Otherwise, the Bug1 algorithm or the Bug2 algorithm is used to plan the path for obstacle avoidance. After leaving the unknown obstacle, the USV returns to the original planned path to continue its search.

[0015] S6: The search mission ends when the unmanned surface vessel has searched the entire search area.

[0016] Furthermore, in S2, the equations of motion for the unmanned surface vessel system model are set as follows:

[0017]

[0018] In the formula: x is the longitudinal displacement of the unmanned surface vessel, y is the lateral displacement of the unmanned surface vessel, μ is the longitudinal velocity of the unmanned surface vessel, v is the lateral velocity of the unmanned surface vessel, ψ is the heading angle, and r is the turning angular velocity.

[0019] Furthermore, in S3,

[0020] S31: Determine the width of the search area, and determine the search direction based on the width of the search area:

[0021] 1) If the search area is a rectangle, then the width of the rectangle is the width of the search area;

[0022] 2) If the search area is a convex polygon, the width of the convex polygon search area is calculated as follows: Let the vertices of the convex polygon be P = {p1, p2, ..., p...} n}, with sides S = {S1, S2, ..., S} n}, calculate the distance D from each edge to all vertices except the two vertices on that edge. p3-s1 D p4-s1 D pn-s1 Take the maximum value as the span D of each side. s1 =max{D p3-s1 D p4-s1 D pn-s1}, taking the minimum value of the span as the width W of the convex polygon = min{D si |i=1,2,…,n};When performing global path planning, the search direction is either the same as or opposite to the width direction of the search region;

[0023] S32: Set the interval width D between two parallel line paths in the search area according to the width of the square within the detection range of the unmanned surface vessel (USV), which is the width of the area scanned when the USV travels straight along the parallel line path.

[0024] Furthermore, in step S4, when performing local path planning using the artificial potential field method based on the known obstacle information within the search area provided by the electronic nautical chart, a repulsive potential field function U is constructed. o (X), and consider the circular area with the unmanned surface vessel's position as the center and τ as the radius as the area where the unmanned surface vessel is located, i.e., the prohibited zone. Let the safe distance of the unmanned surface vessel be D. safe The maximum detection range of the unmanned surface vessel's sensor is D. sen Multiple obstacle avoidance decision zones are set up for unmanned surface vessels, including:

[0025] Let τ < d(X, X o )≤D safe The ring-shaped area is designated as the emergency expansion zone; D safe <d(X, X o )≤D s The circular area is designated as a conventional obstacle avoidance zone, where D... s =D sen -D safe D s <d(X, X o )≤D sen The annular region is designated as the emergency contraction zone; d(X, X) is defined as the annular region. o )>D sen The area is designated as a safe zone;

[0026] Each unmanned surface vessel (USV) obstacle avoidance decision zone is configured with a corresponding partitioned repulsive potential field function, wherein the repulsive potential field function U... o (X) can characterize the distance relationship between the unmanned surface vessel and the target point d(X, X). g The corresponding formula is:

[0027]

[0028] In the formula, U o (X) is the repulsive potential field function; k o d(X, X) is the gain coefficient; o ) represents the distance between the unmanned surface vessel and the obstacle; d represents the distance between the unmanned surface vessel and the obstacle. o The distance affected by the repulsive force of the obstacle; d(X, X g ) represents the distance between the unmanned surface vessel and the target point.

[0029] Furthermore, in step S5, the unmanned surface vessel first obtains the coordinates of the target or unknown obstacle in the sensor coordinate system through sensors, and then converts the coordinates of the target or unknown obstacle in the sensor coordinate system to the coordinates of the target or unknown obstacle in the global coordinate system. The specific steps are as follows:

[0030] S51: Assume the sensor is located at point (x) in the ship's coordinate system. r At point (0), the coordinates of the unknown obstacle in the sensor coordinate system are (d, θ1). According to the coordinate transformation formula, the coordinates of the unknown obstacle in the sensor coordinate system are first converted to coordinates (x′, y′) in the ship's coordinate system. The corresponding coordinate transformation formula is:

[0031]

[0032] S52: The coordinates of the unknown obstacle in the ship's coordinate system are obtained, based on the global coordinates (x) of the unmanned surface vessel. u y u The coordinate transformation formula is used to convert the coordinates (x, y) of the unknown obstacle in the global coordinate system. b y b The corresponding coordinate transformation formula is:

[0033]

[0034] In the formula, α u It is the angle between the unmanned surface vessel's (USV) direction of travel and the direction of the global coordinate system O0x0 axis.

[0035] Furthermore, in S5,

[0036] When an unmanned surface vessel (USV) detects an unknown obstacle through its sensors and is able to detect the boundary of the unknown obstacle, if the USV can find the obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system, it can use the artificial potential field method to plan a path for obstacle avoidance.

[0037] If the unmanned surface vessel (USV) cannot find the obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system, that is, if the USV detects the unknown obstacle through its sensors and the boundary L of the unknown obstacle in the Ox axis direction of the ship's coordinate system is within the range of the USV's coordinates... x Beyond the detection range of the unmanned surface vessel, i.e., L x >(D) sen -D safe When the unmanned surface vessel detects an unknown obstacle in its forward direction, the boundary length L of the obstacle located to the right of the origin O in the Oy axis direction of the ship's coordinate system is considered. y_right The boundary length L located to the left of the origin O y_left The comparison between the width D of the scanned area when the unmanned surface vessel travels straight along a parallel path and the selection of whether to use the Bug1 or Bug2 algorithm for obstacle avoidance, specifically includes:

[0038] Method 1: When the sensor detects an unknown obstacle L y_right ≥D / 2 and L y_left When the distance is less than D / 2, the unmanned surface vessel (USV) uses the Bug2 algorithm to escape the unknown obstacle. The m-line is set as the global path. The USV chooses to turn left to navigate around the unknown obstacle. When it encounters the m-line again, it leaves the unknown obstacle and returns to the original planned path to continue its journey.

[0039] Method 2: When the sensor detects an unknown obstacle L y_right <D / 2 and L y_left When the value is ≥D / 2, the unmanned surface vessel (USV) uses the Bug2 algorithm to get away from the unknown obstacle. The m-line is set as the global path. The USV chooses to turn to the right to bypass the unknown obstacle. When it encounters the m-line again, it leaves the unknown obstacle and returns to the original planned path to continue sailing.

[0040] Method 3: When the sensor detects an unknown obstacle L y_right <D / 2 and L y_left When the distance is less than D / 2, the unmanned surface vessel (USV) uses the Bug1 algorithm to bypass the unknown obstacle. The m-line is set as the global path. After the USV bypasses the unknown obstacle once, it returns to the starting position and records the route lengths L1 and L2 before and after encountering the m-line. If L1 > L2, the USV travels along the path of length L1; otherwise, it travels along the path of length L2. When the USV encounters the m-line again, it leaves the unknown obstacle and returns to the original planned path to continue its journey.

[0041] Furthermore, in S5, when the unmanned surface vessel (USV) is navigating within the search area according to the determined original planned path, a rule is set to determine whether the USV enters a deadlock state during navigation. If the USV is determined to have entered a deadlock state, i.e.:

[0042] <F a (X), F o (X)>=acos(dot(F a (X), F o (X)) / (norm(F a (X))*norm(F o (X))))*180 / pi

[0043]

[0044]

[0045] At this point, a random deflection angle θ2 is set for the unmanned surface vessel, with θ2 ranging from [0, 90°], to allow the unmanned surface vessel to escape the deadlock state, i.e.:

[0046] F a ′(X)=cos -1 θ2*F a (X)

[0047] In the formula, F a (X) represents the gravitational pull of the unmanned surface vessel, F a F'(X) represents the gravitational force on the unmanned surface vessel (USV) after it has randomly deflected by an angle θ2. o (X) represents the repulsive force of the unmanned surface vessel. This indicates the direction of travel for the unmanned surface vessel.

[0048] Beneficial effects: This invention uses a parallel line scanning search method to plan the global path and an improved artificial potential field method to plan the local path. During the unmanned surface vessel's (USV) navigation according to the original planned path, the USV's sensors acquire environmental information in real time to detect unknown obstacles. When approaching unknown obstacles, a combination of multiple obstacle avoidance algorithms is used to select different obstacle avoidance methods according to different unknown obstacles. This ensures the safe and autonomous navigation of the USV while meeting the requirement of uniform coverage of the search area, solving the problem of target omission caused by the inability to uniformly cover the search area. Attached Figure Description

[0049] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 This is a flowchart of the steps in the maritime search area coverage path planning method based on unmanned surface vessels in this invention;

[0051] Figure 2 This is a schematic diagram of the vertical and horizontal viewing angles detected by the unmanned surface vessel's sensor in this invention.

[0052] Figure 3 This is a schematic diagram showing the width of the area scanned by the unmanned surface vessel when it travels straight along a parallel path in this invention.

[0053] Figure 4 This is a schematic diagram of the multiple obstacle avoidance decision zones set in this invention;

[0054] Figure 5a This is a schematic diagram of the unmanned surface vessel detecting the obstacle avoidance target point in this invention;

[0055] Figure 5b This is a schematic diagram showing that the unmanned surface vessel failed to detect the obstacle avoidance target point in this invention;

[0056] Figure 6 This is a flowchart of the obstacle avoidance process of the unmanned surface vessel based on the Bug1 and Bug2 algorithms in this invention;

[0057] Figure 7 This is a schematic diagram illustrating how the unmanned surface vessel (USV) uses the Bug2 algorithm to turn left in this invention.

[0058] Figure 8 This is a schematic diagram illustrating how the unmanned surface vessel (USV) uses the Bug2 algorithm to turn right in this invention.

[0059] Figure 9 This is a schematic diagram illustrating the unmanned surface vessel (USV) in this invention that selects its navigation path after circling around an unknown obstacle using the Bug1 algorithm. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0061] In this invention, a two-level planning approach is employed. First, using known environmental information, a global path is planned using a parallel line scanning search method, and a modified artificial potential field method is used to perform static obstacle avoidance for known obstacles, thus constructing a static route. During the unmanned surface vessel's (USV) navigation, unknown obstacles can render the originally planned path inaccessible. Therefore, the USV uses sensors to acquire environmental information in real time during navigation, perceives unknown obstacles, and employs a combination of multiple obstacle avoidance algorithms when approaching unknown obstacles. Different obstacle avoidance methods are adopted to efficiently avoid obstacles while meeting the coverage requirements of the search area during obstacle avoidance, thereby constructing a dynamic route. Finally, through a two-level obstacle avoidance method of global and local approaches, the safe and autonomous navigation of the USV is ensured.

[0062] Based on the above principles, this embodiment provides a method for maritime search area coverage path planning based on unmanned surface vessels, such as... Figure 1 As shown, the specific steps are as follows:

[0063] S1: Obtain the search area at sea and read the electronic nautical chart information of the search area;

[0064] S2: Construct an unmanned surface vessel system model based on the ship's coordinate system and the global coordinate system;

[0065] The ship's coordinate system O-xyz is a rectangular coordinate system with the origin O at the symmetrical points of the unmanned surface vessel (USV) in all directions. It is fixed on the ship's hull and moves with the USV. The direction of the Ox axis is set as the direction of the USV's navigation. The direction of the Oy axis is set as 90° clockwise. The Oz axis is perpendicular to the waterline.

[0066] The ground coordinate system, also known as the global coordinate system O0-x0y0z0, is an inertial coordinate system fixed on the Earth's surface. Its position can be arbitrarily selected. The O0x0 axis is defined to be in the horizontal plane, and its direction can be arbitrarily selected. Once selected, it is fixed. Rotating the O0x0 axis 90° clockwise gives the direction of the O0y0 axis, and the O0z0 axis is perpendicular to the horizontal plane.

[0067] In this embodiment, the following assumptions are made: the influence of the Earth's curvature is ignored, and the sea surface is considered as a plane; the change in the Z-axis direction is ignored, and the unmanned surface vessel only moves in the XY direction; the influence of wind, waves, and currents on the navigation of the unmanned surface vessel is not considered.

[0068] The equations of motion for the unmanned surface vessel system model are set as follows:

[0069]

[0070] In the formula: x is the longitudinal displacement of the unmanned surface vessel, y is the lateral displacement of the unmanned surface vessel, μ is the longitudinal velocity of the unmanned surface vessel, v is the lateral velocity of the unmanned surface vessel, ψ is the heading angle, and r is the bow angular velocity.

[0071] S3: Determine the search direction and perform global path planning for the search area based on parallel line scanning search. Set the interval width between two parallel line paths in the search area, that is, the width of the area scanned when the unmanned surface vessel travels straight along the parallel line path is D.

[0072] S4: Based on the known obstacle information within the search area provided by the electronic nautical chart, when performing local path planning using the artificial potential field method, a repulsive potential field function U is constructed. o (X), multiple unmanned surface vessel (USV) obstacle avoidance decision zones are set, and a corresponding repulsive potential field function is configured for each USV obstacle avoidance decision zone; wherein, the repulsive potential field function U o (X) can characterize the distance relationship between the unmanned surface vessel and the target point d(X, X). g );

[0073] S5: The unmanned surface vessel navigates within the search area according to the original planned path determined by global path planning and local path planning, and detects targets and unknown obstacles through sensors.

[0074] When a target is detected, the target coordinates in the global coordinate system are sent to shore-based or search and rescue vessels, and the vessel continues to navigate along the original planned path to search for the target.

[0075] When an unknown obstacle is detected, the unmanned surface vessel (USV) determines whether there is an obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system. If there is an obstacle avoidance target point, the artificial potential field method is used to plan the path for obstacle avoidance. Otherwise, the Bug1 algorithm or the Bug2 algorithm is used to plan the path for obstacle avoidance. After leaving the unknown obstacle, the USV returns to the original planned path to continue its search.

[0076] In this embodiment, when the unmanned surface vessel (USV) is navigating within the search area according to the determined original planned path, a rule is set to determine whether the USV enters a deadlock state during navigation. If the USV is determined to have entered a deadlock state, that is:

[0077] <F a (X), F o (X)>=acos(dot(F a (X), F o (X)) / (norm(F a (X))*norm(F o (X))))*180 / pi

[0078]

[0079]

[0080] At this point, a random deflection angle θ2 is set for the unmanned surface vessel, with θ2 ranging from [0, 90°], to allow the unmanned surface vessel to escape the deadlock state, i.e.:

[0081] F a ′(X)=cos -1 θ2*F a (X)

[0082] In the formula, F a (X) represents the gravitational pull of the unmanned surface vessel, F a F'(X) represents the gravitational force on the unmanned surface vessel (USV) after it has randomly deflected by an angle θ2. o (X) represents the repulsive force of the unmanned surface vessel. This indicates the direction of travel for the unmanned surface vessel.

[0083] S6: The search mission ends when the unmanned surface vessel has searched the entire search area.

[0084] In a specific embodiment, in step S3,

[0085] S31: Determine the width of the search area, and determine the search direction based on the width of the search area:

[0086] 1) If the search area is a rectangle, then the width of the rectangle is the width of the search area;

[0087] 2) If the search area is a convex polygon, the width of the convex polygon search area is calculated as follows: Let the vertices of the convex polygon be P = {p1, p2, ..., p...} n}, with sides S = {S1, S2, ..., S} n}, calculate the distance D from each edge to all vertices except the two vertices on that edge. p3-s1 D p4-s1 D pn-s1 Take the maximum value as the span D of each side. s1 =max{D p3-s1 D p4-s1 D pn-s1}, taking the minimum value of the span as the width W of the convex polygon = min{D si |i = 1, 2, ..., n};

[0088] When performing global path planning, the search direction should be aligned with or opposite to the direction of the width of the corresponding search area to achieve coverage of the search area with the fewest turns.

[0089] In practice, if the search area is a concave polygon, the concave polygon is first divided into several convex polygons, and then the search direction is determined by referring to the convex polygons for path planning.

[0090] S32: When performing global route planning, such as Figure 3 As shown, the interval width D between two parallel line paths in the search area is set according to the width of the square within the detection range of the unmanned surface vessel (USV). This is the width of the area scanned by the USV when it travels straight along the parallel line path, ensuring the search coverage of the sensor.

[0091] In this embodiment, considering the motion characteristics of the unmanned surface vessel, a Bezier transition curve is constructed and smoothed for the handling of turning points and turning points.

[0092] Because the traditional artificial potential field method is prone to getting stuck in local minima and the target becomes unreachable, and its application in search path planning requires meeting the requirement of area coverage, this embodiment makes the following improvements to the artificial potential field method:

[0093] Based on the known obstacle information within the search area provided by the electronic nautical chart, when performing local path planning using the artificial potential field method, a repulsive potential field function U is constructed. o (X), and consider the circular area with the unmanned surface vessel's position as the center and τ as the radius as the area where the unmanned surface vessel is located, i.e., the prohibited zone. Let the safe distance of the unmanned surface vessel be D. safe The maximum detection range of the unmanned surface vessel's sensor is D. sen Multiple obstacle avoidance decision zones are set up for unmanned surface vessels, including:

[0094] Let τ < d(X, X o )≤D safe The ring-shaped area is designated as the emergency expansion zone, and D is... safe <d(X, X o )≤D s The circular area is designated as a standard obstacle avoidance zone, where D... s =D sen -D safe D s <d(X, X o )≤D sen The annular region is set as the emergency contraction zone, and d(X, X) is set as the emergency contraction zone. o )>D sen The area is designated as a safe zone, and each unmanned surface vessel (USV) obstacle avoidance decision zone is configured with its corresponding partition repulsive potential field function, wherein the repulsive potential field function U... o (X) can characterize the distance relationship between the unmanned surface vessel and the target point d(X, X). g The corresponding formula is:

[0095]

[0096] In the formula, U o (X) is the repulsive potential field function; k o d(X, X) is the gain coefficient;o ) represents the distance between the unmanned surface vessel and the obstacle; d represents the distance between the unmanned surface vessel and the obstacle. o The distance affected by the repulsive force of the obstacle; d(X, X g () represents the distance between the unmanned surface vessel and the target point;

[0097] In this embodiment, the distance relationship d(X, X) between the unmanned surface vessel and the target point is expressed as follows: g Introducing the repulsive potential field function U o In (X), that is:

[0098]

[0099] The repulsive force of the obstacle on the unmanned surface vessel (USV) gradually decreases as the USV approaches the target position, and the net force moves in the direction of gravity, enabling the USV to always move towards the target position.

[0100] like Figure 4 As shown, the safe zone is the distance d(X, X) between the unmanned surface vessel and the obstacle. o () greater than the maximum detection range D of the unmanned surface vessel sensor sen In areas where the distance between the unmanned surface vessel and obstacles is relatively large, obstacle avoidance is not required;

[0101] Standard obstacle avoidance zone: In this zone, the distance between the unmanned surface vessel and obstacles is appropriate, and there is no need to adjust the repulsion coefficient function;

[0102] Emergency contraction zone: When an obstacle is about to leave the detection range of the UAV's sensors, in order to prevent the obstacle from leaving the UAV's detection range, the repulsive potential field function needs to be adjusted to reduce the repulsive force on the UAV.

[0103] Emergency Expansion Zone: When an obstacle intrudes into the safety zone of the unmanned surface vessel (USV) and there is a real risk of collision, in order to prevent the USV from colliding with the obstacle in this zone, it is necessary to adjust the repulsive potential field function to increase the repulsive force on the USV and keep it away from the obstacle.

[0104] In a specific embodiment, in step S5, such as Figure 2 As shown, the unmanned surface vessel (USV) first obtains the coordinates of the target or unknown obstacle in the sensor coordinate system through its sensors, and then converts the coordinates of the target or unknown obstacle in the sensor coordinate system to the coordinates of the target or unknown obstacle in the global coordinate system. The specific steps are as follows:

[0105] S51: Assume the sensor is located at point (x) in the ship's coordinate system. rAt position 0, during the unmanned surface vessel's (USV) navigation, the sensor's coordinate system remains fixed relative to the vessel's coordinate system. The USV's sensors can measure the azimuth and distance of a target or unknown obstacle relative to the USV. If the unknown obstacle's coordinates in the sensor coordinate system are (d, θ1), the coordinates of the unknown obstacle in the sensor coordinate system are first converted to (x′, y′) in the vessel's coordinate system according to the coordinate transformation formula. The corresponding coordinate transformation formula is:

[0106]

[0107] S52: The coordinates of the unknown obstacle in the ship's coordinate system are obtained, based on the global coordinates (x) of the unmanned surface vessel. u y u The coordinate transformation formula is used to convert the coordinates (x, y) of the unknown obstacle in the global coordinate system. b y b The corresponding coordinate transformation formula is:

[0108]

[0109] In the formula, α u It is the angle between the unmanned surface vessel's (USV) direction of travel and the direction of the global coordinate system O0x0 axis.

[0110] In this embodiment, a multi-sensor fusion method is used to detect targets and unknown obstacles, thereby improving detection accuracy and thus improving the efficiency of the search process.

[0111] Since unknown obstacles can change the situation during the unmanned surface vessel's navigation, and the original planned path may become an unreachable area due to the intrusion of unknown obstacles, a local obstacle avoidance method is adopted when approaching dynamic obstacles to complete local dynamic obstacle avoidance of unknown obstacles.

[0112] In a specific embodiment, in step S5, when an unknown obstacle is detected, the unmanned surface vessel determines whether there is a clear obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system and selects different methods for obstacle avoidance:

[0113] like Figure 5a As shown, when an unmanned surface vessel (USV) detects an unknown obstacle through its sensors and is able to detect the boundary of the unknown obstacle, if the USV can find the obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system, it can use the artificial potential field method to plan the path for obstacle avoidance. However, the artificial potential field method is based on path planning with an accurate target point. When the size of the unknown obstacle exceeds the detection range of the USV, it is impossible to confirm the boundary of the unknown obstacle in the navigation direction, and thus it is impossible to obtain a clear obstacle avoidance target point.

[0114] like Figure 5bAs shown, if the unmanned surface vessel (USV) cannot find the obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system, that is, if the USV detects the unknown obstacle through its sensors and the boundary L of the unknown obstacle in the Ox axis direction of the ship's coordinate system is within the range of the USV's coordinates, then the USV is considered to have detected the unknown obstacle. x Beyond the detection range of the unmanned surface vessel, i.e., L x >(D) sen -D safe When the unmanned surface vessel detects an unknown obstacle in its forward direction, the boundary length L of the obstacle located to the right of the origin O in the Oy axis direction of the ship's coordinate system is considered. y_right The boundary length L located to the left of the origin O y_left The comparison between the width D of the scanned area when the unmanned surface vessel (USV) travels straight along a parallel path determines whether to use the Bug1 or Bug2 algorithm for obstacle avoidance. The Bug1 algorithm is computationally simple and does not require knowledge of the global map or the shape of obstacles. To meet the coverage requirements of the search area when the USV avoids unknown obstacles, this embodiment improves the existing Bug1 algorithm and proposes different obstacle avoidance methods based on the improved Bug1 algorithm, such as... Figure 6 As shown, it specifically includes;

[0115] Method 1: such as Figure 7 As shown, when the sensor detects an unknown obstacle L... y_right ≥D / 2 and L y_left When the distance is less than D / 2, the unmanned surface vessel (USV) uses the Bug2 algorithm to escape the unknown obstacle. The m-line is set as the global path. The USV chooses to turn left to navigate around the unknown obstacle. When it encounters the m-line again, it leaves the unknown obstacle and returns to the original planned path to continue its journey.

[0116] Method 2: such as Figure 8 As shown, when the sensor detects an unknown obstacle L... y_right <D / 2 and L y_left When the value is ≥D / 2, the unmanned surface vessel (USV) uses the Bug2 algorithm to get away from the unknown obstacle. The m-line is set as the global path. The USV chooses to turn to the right to bypass the unknown obstacle. When it encounters the m-line again, it leaves the unknown obstacle and returns to the original planned path to continue sailing.

[0117] Method 3: such as Figure 9 As shown, when the sensor detects an unknown obstacle L y_right <D / 2 and L y_leftWhen the distance is less than D / 2, the unmanned surface vessel (USV) uses the Bug1 algorithm to bypass the unknown obstacle. The m-line is set as the global path. After the USV bypasses the unknown obstacle once, it returns to the starting position and records the route lengths L1 and L2 before and after encountering the m-line. If L1 > L2, the USV travels along the path of length L1; otherwise, it travels along the path of length L2. When the USV encounters the m-line again, it leaves the unknown obstacle and returns to the original planned path to continue its journey.

[0118] In this embodiment, the original planned global path, i.e., the parallel line path, is set as m-line, and m-line will not change as the unmanned surface vessel moves.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for planning a maritime search area coverage path based on an unmanned surface vessel, characterized in that, The specific steps are as follows: S1: Obtain the search area at sea and read the electronic nautical chart information of the search area; S2: Construct an unmanned surface vessel system model based on the ship's coordinate system and the global coordinate system; S3: Determine the search direction and perform global path planning for the search area based on parallel line scanning search. Set the interval width between two parallel line paths in the search area, that is, the width of the area scanned when the unmanned surface vessel travels straight along the parallel line path is D. S4: Based on the known obstacle information within the search area provided by the electronic nautical chart, when performing local path planning using the artificial potential field method, a repulsive potential field function is constructed. Multiple obstacle avoidance decision zones are set up, and a corresponding repulsive potential field function is configured for each obstacle avoidance decision zone; wherein, the repulsive potential field function Capable of representing the distance relationship between the unmanned surface vessel and the target point ; S5: The unmanned surface vessel navigates within the search area according to the original planned path determined by global path planning and local path planning, and detects targets and unknown obstacles through sensors. When a target is detected, the target coordinates in the global coordinate system are sent to shore-based or search and rescue vessels, and the vessel continues to navigate along the original planned path to search for the target. When an unknown obstacle is detected, the unmanned surface vessel (USV) determines whether there is an obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system. If there is an obstacle avoidance target point, the artificial potential field method is used to plan the path for obstacle avoidance. Otherwise, the Bug1 algorithm or the Bug2 algorithm is used to plan the path for obstacle avoidance. After leaving the unknown obstacle, the USV returns to the original planned path to continue its search. S6: The search mission ends when the unmanned surface vessel has searched the entire search area.

2. The maritime search area coverage path planning method based on unmanned surface vessels according to claim 1, characterized in that, In S2, the equations of motion for the unmanned surface vessel system model are set as follows: ； In the formula: For the longitudinal displacement of the unmanned surface vessel, For the lateral displacement of the unmanned surface vessel, Let the longitudinal velocity of the unmanned surface vessel be . The lateral speed of the unmanned surface vessel, For the heading angle, This is the angular velocity of the bow.

3. The maritime search area coverage path planning method based on unmanned surface vessels according to claim 1, characterized in that, In S3, S31: Determine the width of the search area, and determine the search direction based on the width of the search area: 1) If the search area is a rectangle, then the width of the rectangle is the width of the search area; 2) If the search area is a convex polygon, the width of the convex polygon search area is calculated as follows: The vertices of the convex polygon are set as... Each side is Calculate the distance from each edge to all vertices except the two vertices on that edge. Take the maximum value as the span of each edge. The minimum value in the span is taken as the width of the convex polygon. ; When performing global path planning, the search direction is either the same as or opposite to the width of the search area. S32: Set the interval width D between two parallel line paths in the search area according to the width of the square within the detection range of the unmanned surface vessel (USV), which is the width of the area scanned when the USV travels straight along the parallel line path.

4. The maritime search area coverage path planning method based on unmanned surface vessels according to claim 1, characterized in that, In step S4, when performing local path planning using the artificial potential field method based on the known obstacle information within the search area provided by the electronic nautical chart, a repulsive potential field function is constructed. And will use the unmanned surface vessel's position as the center, A circular area with radius is considered the area where the unmanned surface vessel (USV) is located, i.e., the restricted zone. Let the safe distance for the USV be . The maximum detection range of the unmanned surface vessel's sensor is Multiple obstacle avoidance decision zones are set up for unmanned surface vessels, including: Will The ring-shaped area is designated as the emergency expansion zone; The circular area is designated as a standard obstacle avoidance zone, in which... ;Will The annular area is designated as the emergency contraction zone; The area is designated as a safe zone; Each unmanned surface vessel (USV) obstacle avoidance decision zone is configured with a corresponding partitioned repulsive potential field function, wherein the repulsive potential field function... Capable of representing the distance relationship between the unmanned surface vessel and the target point The corresponding formula is: ； In the formula, Let be the repulsive potential field function; This is the gain coefficient; The distance between the unmanned surface vessel and the obstacle; The distance at which the repulsive force of the obstacle is exerted; This represents the distance between the unmanned surface vessel and the target point.

5. The maritime search area coverage path planning method based on unmanned surface vessels according to claim 4, characterized in that, In step S5, the unmanned surface vessel first obtains the coordinates of the target or unknown obstacle in the sensor coordinate system through sensors, and then converts the coordinates of the target or unknown obstacle in the sensor coordinate system to the coordinates of the target or unknown obstacle in the global coordinate system. The specific steps are as follows: S51: Assume the sensor is located at a point in the ship's coordinate system. At this location, the coordinates of the unknown obstacle in the sensor coordinate system are: According to the coordinate transformation formula, the coordinates of the unknown obstacle in the sensor coordinate system are first converted to the coordinates in the ship's coordinate system. The corresponding coordinate transformation formula is: ； S52: The coordinates of the unknown obstacle in the ship's coordinate system, based on the global coordinates of the unmanned surface vessel. Using coordinate transformation formulas, the coordinates of the unknown obstacle are converted to the coordinates in the global coordinate system. The corresponding coordinate transformation formula is: ； In the formula, The unmanned surface vessel's navigation direction and global coordinate system The angle along the axial direction.

6. The maritime search area coverage path planning method based on unmanned surface vessels according to claim 1, characterized in that, In S5, When an unmanned surface vessel (USV) detects an unknown obstacle through its sensors and is able to detect the boundary of the unknown obstacle, if the USV can find the obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system, it can use the artificial potential field method to plan a path for obstacle avoidance. If the unmanned surface vessel (USV) cannot find the obstacle avoidance target point based on the coordinates of the unknown obstacle in the global coordinate system, that is, if the USV detects the unknown obstacle through its sensors and the unknown obstacle is within the ship's coordinate system... Axial boundary It was beyond the detection range of the unmanned surface vessel, that is... At that time, based on the unknown obstacles detected by the unmanned surface vessel in its direction of travel within the ship's coordinate system... The axial direction is located at the origin. right boundary length Located at the origin left boundary length The comparison between the width D of the scanned area when the unmanned surface vessel travels straight along a parallel path and the selection of whether to use the Bug1 or Bug2 algorithm for obstacle avoidance, specifically including: Method 1: When the sensor detects an unknown obstacle and When the unmanned surface vessel (USV) uses the Bug2 algorithm to get away from the unknown obstacle, it sets the m-line as the global path, turns to the left to navigate around the unknown obstacle, and leaves the unknown obstacle when it encounters the m-line again, and returns to the original planned path to continue its journey. Method 2: When the sensor detects an unknown obstacle and When the unmanned surface vessel (USV) uses the Bug2 algorithm to get away from the unknown obstacle, it sets the m-line as the global path, turns to the right to navigate around the unknown obstacle, and leaves the unknown obstacle when it encounters the m-line again, and returns to the original planned path to continue its journey. Method 3: When the sensor detects an unknown obstacle and When the unmanned surface vessel (USV) uses the Bug1 algorithm to bypass the unknown obstacle, it sets m-line as the global path. After the USV bypasses the unknown obstacle once, it returns to the starting position and records the route lengths L1 and L2 before and after encountering m-line. If L1 > L2, the USV travels along the path of length L1; otherwise, it travels along the path of length L2. When the USV encounters m-line again, it leaves the unknown obstacle and returns to the original planned path to continue its journey.

7. The maritime search area coverage path planning method based on unmanned surface vessels according to claim 1, characterized in that, In S5, when the unmanned surface vessel (USV) is navigating within the search area according to the determined original planned path, a rule is set to determine whether the USV enters a deadlock state during navigation. If the USV is determined to have entered a deadlock state, i.e.: ； At this point, a random yaw angle for the unmanned surface vessel is set. , The range of values ​​is This allows the unmanned surface vessel to escape the deadlock state, that is: ； In the formula, For the gravity of the unmanned surface vessel, To set the random yaw angle of the unmanned surface vessel The gravity of the unmanned surface vessel behind it The repulsive force of the unmanned surface vessel, This indicates the direction of travel for the unmanned surface vessel.

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