An unmanned ship autonomous obstacle avoidance method based on artificial electric field lines

Abstract

The application provides an unmanned ship autonomous obstacle avoidance method based on artificial electric field lines, which utilizes the distribution characteristics of electric field lines to search for obstacles in a certain area in front of the unmanned ship and determine whether to keep the current heading to continue driving forward, and the specific method comprises the following steps: data initialization; setting a safe distance range to search for obstacles; judging whether the unmanned ship has passed several obstacles; calculating the closest obstacle to the unmanned ship and giving priority to avoiding; calculating the change of the electric field in front of the unmanned ship within a certain distance between the obstacle and the non-obstacle to obtain an angle; performing rudder selection; adjusting the heading of the unmanned ship according to the electric field change angle; updating the positions and motion states of the unmanned ship and the obstacles, and repeating the above steps until the end point is reached. According to the distribution characteristics of the electric field lines, the path of the unmanned ship is planned, the situation that the traditional method is trapped in a local optimal solution and low efficiency is avoided, and effective protection is provided for the obstacle avoidance of the unmanned ship at sea.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of unmanned ships, and particularly relates to an unmanned ship autonomous obstacle avoidance method based on artificial electric field lines. BACKGROUND

[0002] An unmanned ship (USV) is originally designed to remove mines and obstacles in a broken wave zone. With the development of new technologies such as computers and artificial intelligence, unmanned ships have been widely used in military, civilian and other fields, and can carry different sensors and equipment to perform tasks such as surveillance and reconnaissance, anti-submarine, search and rescue, collection of weather and water information or geographic survey. China started late in the research and development of unmanned ships, although there is a certain gap with internationally advanced unmanned ship technology, but through continuous research efforts and active development of unmanned ships, a variety of unmanned ships such as "Tianxiang No. 1" and "Haiteng" series have been developed, and have been widely used in the fields of weather detection, ocean development and construction, water search and rescue and monitoring in China.

[0003] The path planning technology of an unmanned ship is similar to the path planning of a robot such as an unmanned vehicle, a drone or a manipulator. In an application scenario that is not completely known, in the presence of static and dynamic obstacles, a collision-free path from a known point to a target is found according to certain evaluation criteria, so that the unmanned ship can safely and reliably avoid all obstacles. There are various research algorithms for unmanned ship path planning in the prior art, such as artificial potential field method, A-star algorithm, particle swarm algorithm, genetic algorithm and sparse A* algorithm. Although the artificial potential field method is simple, real-time, fast in planning speed and easy to implement, it is difficult to find a path in the presence of similar obstacles, which can easily lead to a local optimal problem. The A-star algorithm is a relatively simple and efficient algorithm, but as the search space increases, the amount of calculation increases exponentially, which can relatively lead to a long planning time. Although the particle swarm algorithm, the genetic algorithm and the sparse A* algorithm have also been widely applied, these planning algorithms more or less have some defects, such as insufficient global search accuracy, non-smooth planning path, slow convergence speed and easy to fall into a local optimal solution. Therefore, the present application proposes an unmanned ship obstacle avoidance research method based on electric field line distribution, which overcomes the defects and deficiencies of the previous unmanned ship path planning algorithm, and has been confirmed by multiple tests that the application of electric field line distribution characteristics in the path planning of unmanned ship obstacle avoidance improves the accuracy and efficiency of path planning and avoids falling into a local optimal solution. SUMMARY

[0004] The unmanned ship autonomous obstacle avoidance method and system based on artificial electric field lines can make full use of the characteristics of electric field line distribution, compare the electric field in a certain area in front of the unmanned ship when there is an obstacle or not, determine whether there is an obstacle, and plan the path of the unmanned ship based on the electric field line distribution, so as to overcome the problems of falling into local optimal solution, slow convergence speed and insufficient accuracy in the prior art.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] An unmanned ship autonomous obstacle avoidance method based on artificial electric field lines, characterized in that:

[0007] Step 1: data initialization; the initialized parameters specifically include: the length L of the unmanned ship, the initial position P0 of the unmanned ship, the target position P1 of the unmanned ship movement, the radius R of the obstacle, the speed v of the obstacle movement, the heading angle θ of the obstacle movement, the movement speed v of the unmanned ship, and the heading angle θ of the unmanned ship; obs obs USV USV ;

[0008] Step 2: set a safe distance range, extend from the position a in front of the heading direction of the bow to the position b, and take this range as the safe distance of the unmanned ship;

[0009] Step 3: determine how many obstacles the unmanned ship passes through in the safe distance range;

[0010] Step 4: calculate and find the minimum distance between the edge point of the obstacle in the safe distance and the bow of the unmanned ship, obtain the obstacle closest to the unmanned ship as the priority avoidance object;

[0011] Step 5: equivalent the obstacle to a circular model, and calculate the change of the electric field modulus value caused by the obstacle;

[0012] Preferably, the spherical mirror image method is adopted, the unmanned ship is regarded as a positive charge, the terminal position is regarded as a negative charge, the obstacle is regarded as a sphere, the change of the electric field modulus value caused by the unmanned ship and the terminal position outside the obstacle is calculated, and it is particularly stated that the obstacle and the unmanned ship are on the water surface, so that only the longitudinal component E x and the transverse component E y of the electric field component are calculated. The calculation method of the electric field generated by a single point charge outside the sphere outside the sphere is as follows:

[0013] The charge amount of the unmanned ship is q, the charge amount of the terminal position is-q, and the distance between the unmanned ship and the sphere center of the i(th) (i=1, 2,..., n) obstacle is d i,USV ​​​The radius of the ith(i=1,2,...,n) obstacle is a i The charge amount of the mirror charge is q' i,USV , q" i,USV The mirror charge q' i,USV The distance from the obstacle to the sphere center is d' i,USV The distance from the end point to the sphere center of the ith(i=1,2,...,n) obstacle is d i,end The radius of the ith(i=1,2,...,n) obstacle is a i The charge amount of the mirror charge is q' i,end , q" i,end The mirror charge q' i,end The distance from the obstacle to the sphere center is d' i,end The mirror charge q" i,end is located at the obstacle sphere center position, the seawater conductivity is σ1, and the obstacle conductivity is σ2, then:

[0014]

[0015] Where k is an intermediate variable, and n is a natural number;

[0016] The mirror charge related parameters of the unmanned ship are:

[0017]

[0018] The mirror charge related parameters of the end point position are:

[0019]

[0020] Let the center coordinates of the unmanned ship be (x USV , y USV ), and the horizontal component of the electric field of the unmanned ship at any position P(x,y) outside the sphere is:

[0021]

[0022] Let the end point position be (x end , y end ), and the horizontal component of the electric field of the end point position at any position P(x,y) outside the sphere is:

[0023]

[0024] Let the sphere center coordinates of the ith(i=1,2,...,n) obstacle be (x i,obs , y i,obs ), then the mirror charge q' i,USV , q" i,USVThe coordinates are:

[0025]

[0026] Let the coordinates of the center of the sphere of the i-th (i = 1, 2, ..., n) obstacle be (x... i,obs ,y i,obs If the endpoint is located in the i-th (i = 1, 2, ..., n) obstacle, then the mirror charge q' of the endpoint is... i,end ,q” i,end The coordinates are:

[0027]

[0028] The mirror charge q' of the unmanned surface vessel in the i-th (i = 1, 2, ..., n) obstacle i,USV ,q” i,USV The endpoint is the mirror image charge q' in the i-th (i = 1, 2, ..., n) obstacle. i,end ,q” i,end The horizontal component of the electric field at any position P(x,y) outside the sphere is:

[0029]

[0030] The horizontal component of the electric field at a point P(x,y) outside the obstacle is the unmanned vessel's own charge q and all its mirror charges q'. i,USV and q” i,USV The charge at the endpoint is -q, and all mirror charges q' are... i,end ,q” i,end The linear superposition is:

[0031]

[0032] The electric field magnitude at a point P(x,y) outside the obstacle is:

[0033]

[0034] Step 6: According to maritime rules, determine the relative motion between the unmanned vessel and the obstacle, and make a steering choice accordingly;

[0035] Preferably, the difference in heading angle between the unmanned vessel and the moving obstacle is described with the heading direction of the unmanned vessel as the reference (i.e., the heading angle is 0°).

[0036] Overtaking: If the angle difference between the unmanned vessel's high-speed travel and the obstacle's heading is between [315°, 360°), and the vessel approaches a dangerous distance, the obstacle should be on the starboard side of the unmanned vessel, meaning the unmanned vessel should travel on the port side. If the angle difference is between [0°, 45°], and the unmanned vessel's speed is greater than the obstacle's speed, it is considered overtaking and should proceed on the port side; otherwise, it should proceed on the right side.

[0037] Head-on encounter: if the included angle is between [165°, 195°] and the distance is close to the dangerous distance, the unmanned ship encounters the obstacle collision, at this time the unmanned ship should pass on the right side.

[0038] Cross encounter: if the included angle is between (45°, 165°) and the distance is close to the dangerous distance, the obstacle crosses on the right side of the unmanned ship, at this time the unmanned ship should pass on the right side; if the included angle is between (195°, 315°) and the distance is close to the dangerous distance, the obstacle crosses on the left side of the unmanned ship, at this time the unmanned ship should pass on the left side

[0039] Step 7: According to the electric field x and y components, the heading adjustment of the unmanned ship is carried out within the actual rudder angle change range of the unmanned ship. The electric field distribution of the unmanned ship at a point P(x, y) outside the obstacle is equivalent to the superposition of 5 point charges, which are placed equidistantly to the head and tail with the center point of the unmanned ship as the midpoint and at an interval of 0.25L; the forward direction of the unmanned ship is calculated to set the search angle c°, the electric field Ex and Ey components at-c° and c° in front of the unmanned ship with obstacles and without obstacles, assuming that the longitudinal component of the electric field at-c° without obstacles is E x0_nobs , the transverse component is E y0_nobs , the longitudinal component of the electric field at-c° with obstacles is E x0_yobs , the transverse component is E y0_yobs ; assuming that the longitudinal component of the electric field at c° without obstacles is E x1_nobs , the transverse component is E y1_nobs , the longitudinal component of the electric field at c° with obstacles is E x1_yobs , the transverse component is E y1_yobs ; θ Δ is the angle adjustment amount, duofu is the rudder direction, here it is specified that right rudder is duofu = 1, and left rudder is duofu =-1, θ k is the heading angle at the kth moment, θ k-1 is the heading angle at the (k-1)th moment, at the same time, according to the limitation of the actual rudder angle change of the unmanned ship, if the calculated heading angle change exceeds 15°, the change is made according to 15°, then the heading angle adjustment method is:

[0040]

[0041] Preferably, considering the turning radius of the actual unmanned ship, the change of the heading angle is limited to not more than 15° each time.

[0042] In step 8, the positions and motion states of the unmanned ship and the obstacles are updated, and the calculation of steps 1-7 is re-performed until the end point is reached, and the obstacle avoidance is completed; here, only the position of the unmanned ship is updated, assuming that the coordinates of the unmanned ship at k-1 time before the update are (x k-1 ,y k-1 ), the speed is v k-1 , the electric field modulus when there is no obstacle in the safety range at this time is E 0,k-1 , the electric field modulus when there is an obstacle is E 1,k-1 , the coordinates of the unmanned ship at k time after the update are (x k ,y k ), the speed is v k , and the heading angle is θ k , the position updating method is as follows:

[0043]

[0044] Preferably, according to the actual sailing rules of the unmanned ship, the maximum change amount v max of the speed is limited to 8 m / s.

[0045] In a second aspect, the present application provides a computer device comprising a memory and a processor, wherein the memory stores a computer program, and wherein the processor implements the artificial electric field line-based autonomous obstacle avoidance method for an unmanned ship as described above when executing the computer program.

[0046] In a third aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program is executed by a processor to implement the artificial electric field line-based autonomous obstacle avoidance method for an unmanned ship as described above.

[0047] Compared with the prior art, the present application has the following beneficial effects:

[0048] The present application provides an artificial electric field line-based autonomous obstacle avoidance method for an unmanned ship, which mainly utilizes the characteristics of the electric field line distribution conforming to the natural law, continuously calculates the electric field distribution between the current position and the target position of the unmanned ship, judges whether there is an obstacle in front of the unmanned ship and the number of obstacles, and continuously updates the position of the unmanned ship according to the above, thereby improving the efficiency and accuracy of identifying obstacles.

[0049] Meanwhile, in the presence of obstacles, the heading angle of the unmanned ship is planned according to the deflection of the unmanned ship before and after passing through the obstacle, which makes the planning result more consistent with the actual scene, greatly improves the obstacle avoidance efficiency of the unmanned ship, ensures the driving safety of the unmanned ship, and avoids local optimal solution. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1The schematic diagram of the path for the unmanned ship to avoid multiple obstacles of the application;

[0051] Figure 2 The schematic diagram of the spherical mirror image method used in the application;

[0052] Figure 3 The electric field distribution between the unmanned ship and the target in the application when there is no obstacle;

[0053] Figure 4 The electric field distribution between the unmanned ship and the target in the application when there is an obstacle;

[0054] Figure 5 The definition diagram of the maritime rule conflict situation;

[0055] Figure 6 The schematic diagram of the path for the unmanned ship to avoid obstacles of the application;

[0056] Figure 7 The electric field line distribution when the unmanned ship moves to x=24m in the application;

[0057] Figure 8 The electric field line distribution when the unmanned ship moves to x=-13m in the application. DETAILED DESCRIPTION

[0058] The application will be further described below with reference to the embodiments shown in the drawings.

[0059] The application provides an unmanned ship autonomous obstacle avoidance method based on artificial electric field lines. In order to make the purpose, technical scheme and effect of the application more clear and explicit, the application will be further described in detail below with reference to the drawings.

[0060] Embodiment one

[0061] For the case where multiple obstacles exist in the actual navigation process, the initialized parameters specifically include: the length L of the unmanned ship, the initial position P0 of the unmanned ship, the target position P1 of the unmanned ship movement, the radius R of the obstacle, the speed v of the obstacle movement obs , the heading angle θ of the obstacle movement obs , the movement speed v of the unmanned ship USV , and the heading angle θ of the unmanned ship USV .

[0062] The safety distance range is set, which is extended from the position a in front of the bow direction to the position b, and this range is taken as the safety distance of the unmanned ship.

[0063] It is judged that how many obstacles the unmanned ship passes through in the safety distance range.

[0064] The minimum distance between the edge point of the obstacle within the safety distance and the bow of the unmanned ship is calculated to obtain the obstacle closest to the unmanned ship as the priority avoidance object.

[0065] The obstacle is equivalent to a circular model, and the change of the electric field modulus caused by the obstacle is calculated.

[0066] Preferably, the spherical mirror method (as shown in Figure 2 ) is used to calculate the change of the electric field modulus caused by the unmanned ship and the terminal position outside the obstacle, and it is particularly pointed out that the obstacle and the unmanned ship are both on the water surface, so that the electric field components are only calculated in the longitudinal component E x and the transverse component E y . The calculation method of the electric field generated by a single point charge outside the sphere outside the sphere is as follows:

[0067] The charge amount of the unmanned ship is q, the charge amount of the terminal position is -q, the distance between the unmanned ship and the sphere center of the i th (i = 1, 2,..., n) obstacle is d i,USV , the radius of the i th (i = 1, 2,..., n) obstacle is a i , the charge amount of the mirror charge is q' i,USV , q” i,USV , the mirror charge q' i,USV is located at a distance d' i,USV from the sphere center of the obstacle, the distance between the terminal position and the sphere center of the i th (i = 1, 2,..., n) obstacle is d i,end , the radius of the i th (i = 1, 2,..., n) obstacle is a i , the charge amount of the mirror charge is q' i,end , q” i,end , the mirror charge q' i,end is located at a distance d' i,end from the sphere center of the obstacle, and the mirror charge q” i,end is located at the sphere center of the obstacle, the sea water conductivity is σ1, and the obstacle conductivity is σ2, then:

[0068]

[0069] wherein k is an intermediate variable, and n is a natural number;

[0070] The mirror charge related parameters of the unmanned ship are:

[0071]

[0072] The mirror charge related parameters of the terminal position are:

[0073]

[0074] Let the center coordinates of the unmanned vessel be (x USV ,y USV The horizontal component of the electric field of the unmanned ship at any position P(x,y) outside the sphere is:

[0075]

[0076] Let the endpoint be (x end ,y end The horizontal component of the electric field at any position P(x,y) outside the sphere, where the endpoint is located, is:

[0077]

[0078] Let the coordinates of the center of the sphere of the i-th (i = 1, 2, ..., n) obstacle be (x... i,obs ,y i,obs If the unmanned surface vessel's mirror charge q' is in the i-th (i = 1, 2, ..., n) obstacle, then... i,USV ,q” i,USV The coordinates are:

[0079]

[0080] Let the coordinates of the center of the sphere of the i-th (i = 1, 2, ..., n) obstacle be (x... i,obs ,y i,obs If the endpoint is located in the i-th (i = 1, 2, ..., n) obstacle, then the mirror charge q' of the endpoint is... i,end ,q” i,end The coordinates are:

[0081]

[0082] The mirror charge q' of the unmanned surface vessel in the i-th (i = 1, 2, ..., n) obstacle i,USV ,q” i,USV The endpoint is the mirror image charge q' in the i-th (i = 1, 2, ..., n) obstacle. i,end ,q” i,end The horizontal component of the electric field at any position P(x,y) outside the sphere is:

[0083]

[0084] The horizontal component of the electric field at a point P(x,y) outside the obstacle is the unmanned vessel's own charge q and all its mirror charges q'. i,USV and q” i,USV The charge at the endpoint is -q, and all mirror charges q' are... i,end ,q” i,end The linear superposition is:

[0085]

[0086] The electric field modulus at a point P(x, y) outside the obstacle is:

[0087]

[0088] According to the maritime rules, the relative motion state between the unmanned ship and the obstacle is judged, and the steering selection is performed.

[0089] Preferably, the heading angle difference between the unmanned ship and the moving obstacle is described based on the heading direction of the unmanned ship (i.e., the heading angle is 0°), as shown in Figure 5 .

[0090] Overtaking: if the heading angle difference between the high-speed sailing unmanned ship and the obstacle is between [315°, 360°) and the dangerous distance is approached, the obstacle should sail on the right side of the unmanned ship, i.e., the left side of the unmanned ship; and if the angle difference is between [0°, 45°] and the unmanned ship speed is greater than the obstacle speed, it is overtaking, then the left side is passed, otherwise the right side is passed.

[0091] Head-on encounter: if the included angle is between [165°, 195°] and the dangerous distance is approached, the unmanned ship encounters and collides with the obstacle, at which time the unmanned ship should pass on the right side.

[0092] Cross encounter: if the included angle is between (45°, 165°) and the dangerous distance is approached, the obstacle encounters on the right side of the unmanned ship, at which time the unmanned ship should pass on the right side; if the included angle is between (195°, 315°) and the dangerous distance is approached, the obstacle encounters on the left side of the unmanned ship, at which time the unmanned ship should pass on the left side.

[0093] According to the electric field x and y components, the unmanned ship heading adjustment is performed within the actual rudder angle change range. The electric field distribution of the unmanned ship is equivalent to five point charges, i.e., the electric field distribution generated by the unmanned ship at a point P(x, y) outside the obstacle is superimposed by five point charges, which are equally spaced to the head and tail sides with the center point of the unmanned ship as the midpoint and at an interval of 0.25L; the forward direction of the unmanned ship is calculated to set the parameter c° as the search angle, the electric field Ex and Ey components at -c° and c° of a certain position in front of the unmanned ship with and without obstacles, assuming that the longitudinal component of the electric field at -c° without obstacles is E x0_nobs , the transverse component is E y0_nobs , the longitudinal component of the electric field at -c° with obstacles is E x0_yobs , and the transverse component is E y0_yobs ; assuming that the longitudinal component of the electric field at c° without obstacles is E x1_nobs , and the transverse component is E y1_nobsThe longitudinal component of the electric field at the point c° when there is an obstacle is E x1_yobs , and the transverse component is E y1_yobs ; θ Δ is the angle adjustment amount, duofu is the rudder direction, and herein, right rudder is defined as duofu = 1, and left rudder is defined as duofu = -1. θ k is the heading angle at the kth moment, and θ k-1 is the heading angle at the (k-1)th moment. Meanwhile, according to the actual restriction of the rudder angle change of the unmanned ship, if the calculated heading angle change exceeds 15°, the change is performed according to 15°, and the adjustment method of the heading angle is as follows:

[0094]

[0095] Preferably, considering the turning radius of the actual unmanned ship, the change of the heading angle is limited to not more than 15° each time.

[0096] The positions and motion states of the unmanned ship and the obstacle are updated, and the calculation of steps 1-7 is performed again until the end point is reached, and the obstacle avoidance is completed. Herein, only the position of the unmanned ship is updated, and the coordinates of the unmanned ship at the (k-1)th moment before the update are (x k-1 , y k-1 ), the speed is v k-1 , the electric field module value when there is no obstacle in the safety range at this time is E 0,k-1 , the electric field module value when there is an obstacle is E 1,k-1 , the coordinates of the unmanned ship at the kth moment after the update are (x k , y k ), the speed is v k , and the heading angle is θ k . The position update method is as follows:

[0097]

[0098] Preferably, according to the actual sailing rules of the unmanned ship, the maximum change amount v max of the speed is limited to 8 m / s.

[0099] Example Two

[0100] For the unmanned ship to avoid a single obstacle, it is assumed that the unmanned ship is positively charged, the target position of the unmanned ship movement is negatively charged, and the obstacle is an insulating sphere without charge. The obstacle avoidance research is based on the electric field line distribution of the positive and negative charges formed by the unmanned ship and the target position around the obstacle. Here, the method is explored based on a simple model. It is assumed that the unmanned ship moves at a constant speed along the X-axis direction from (100, 0) to (-100, 0) at a speed of -2 m / s. Since the distance d1 between the obstacle and the unmanned ship and the distance d2 between the target position and the unmanned ship can be obtained by radar, etc., it is assumed that when d1 = d2, the unmanned ship begins to avoid obstacles.

[0101] Initialize the length L of the unmanned ship, the initial position P0 of the unmanned ship, the target position P1 of the unmanned ship movement, the radius R of the obstacle, and the movement speed v of the unmanned ship.

[0102] Since the unmanned ship and the obstacle are both water surface targets, the space studied is a two-dimensional plane. The sphere radius is set to 5 m, the sphere center coordinates are (0, 0), the initial position coordinates of the unmanned ship are (100, 0), and the target position coordinates of the unmanned ship movement are (-100, 0).

[0103] When there is no obstacle between the unmanned ship and the target, the electric field line distribution is as shown in Figure 3 The right center point represents the initial position of the unmanned ship target, which is positively charged with a charge of 1e-6. The left center point represents the target position of the unmanned ship movement, which is negatively charged with a charge of -1e-6.

[0104] When there is an obstacle between the unmanned ship and the target, the electric field line distribution is as shown in Figure 4 The right center point represents the initial position of the unmanned ship target, which is positively charged with a charge of 1e-6. The left center point represents the target position of the unmanned ship movement, which is negatively charged with a charge of -1e-6.

[0105] Comparing Figure 3 and Figure 4 It can be seen that when there is an obstacle between the unmanned ship and the target position, the electric field line will be distorted near the obstacle, and the electric field line will be pushed away along the outer edge of the obstacle. Based on this, the unmanned ship obstacle avoidance method can be researched based on the phenomenon of electric field line distortion near the obstacle.

[0106] Obtain the electric field distribution; the unmanned ship calculates the electric field distribution between the current position and the target position once every 1 s. In order to avoid collision between the unmanned ship and the obstacle, the electric field distribution of a certain area in front of the unmanned ship without obstacles is compared with the electric field distribution with obstacles. If they are consistent, the current heading is maintained and the unmanned ship continues to move forward. If distortion occurs, the heading is adjusted according to the degree of electric field distortion.

[0107] Here, the adjustment of the heading according to the deflected heading angle is assumed that the total electric field E is the same with or without obstacles, and the heading angle deflected by the unmanned ship to avoid obstacles is θ, and the specific calculation method is as follows:

[0108] (1) When the unmanned ship has not passed through the obstacle, the electric field radiated by the unmanned ship is radiated in the direction of the electric field line in front of the moving direction near the obstacle, and the calculation method of the heading angle is:

[0109]

[0110] where E x,k is the X component of the electric field intensity at time k with obstacles, E y,k is the Y component of the electric field intensity at time k with obstacles, E k is the total electric field intensity at time k, P x,k+1 , P y,k+1 are the X and Y coordinate positions of the unmanned ship at time k+1 with obstacles, P x,k , P y,k are the X and Y coordinate positions of the unmanned ship at time k with obstacles, v x,k , v y,k are the X and Y direction motion speeds of the unmanned ship at time k with obstacles.

[0111] (2) When the unmanned ship has passed through the obstacle, the electric field radiated by the unmanned ship is in the opposite direction of the moving direction near the obstacle, and the calculation method of the heading angle is:

[0112]

[0113] Preferably, considering the turning radius of the actual unmanned ship, the change of the heading angle is limited to not more than 15° each time.

[0114] Preferably, the certain area in front of the unmanned ship is specifically: the area [L / 4, L] in front of the unmanned ship.

[0115] Specifically, real-time judgment is performed when avoiding obstacles. The radar forward search is used as the basis for obtaining obstacles, and 4 times the ship length is used as the safety distance to judge important obstacles within the range of 4L near the USV (unmanned ship), calculate the distance between the suspected obstacle and the bow of the USV, find the obstacle closest to the USV within the safety range, and preferentially avoid it.

[0116] The change of the heading angle is adjusted by the electric field modulus; the electric field modulus of the USV equivalent circle caused by the obstacle is calculated, and under normal circumstances, the USV should advance in the direction of the maximum electric field modulus, and when encountering an obstacle, the heading angle should be adjusted in the direction of the minimum electric field modulus, which is equivalent to choosing the opposite direction of the obstacle.

[0117] In addition, when avoiding obstacles, both static and dynamic obstacles need to be considered. For dynamic obstacles, reference is made to the International Regulations for Preventing Collisions At Sea, which is described in detail as follows:

[0118] In order to avoid threats to the safety of other ships, personnel and property on the sea and the safety of the unmanned ship itself, the unmanned ship must meet certain rules during obstacle avoidance. The International Regulations for Preventing Collisions At Sea (1972 / COLREGS) is a maritime traffic rule formulated by the International Maritime Organization to prevent and avoid collisions between ships. However, there is no specific law or regulation to guide the navigation behavior of the unmanned ship on the water surface. A more reasonable solution is to make the unmanned ship comply with the International Regulations for Preventing Collisions At Sea. Articles 13, 14 and 15 of the International Regulations for Preventing Collisions At Sea make provisions for the collision scenarios that may occur during the navigation of the unmanned ship: overtaking, head-on meeting and crossing meeting. However, these rules are only a behavioral constraint for ship operation and do not explicitly specify the angle and range in actual application.

[0119] The invention will give specific instructions for the relevant regulations of the International Regulations for Preventing Collisions At Sea based on the actual situation of the unmanned ship, as shown in the definition of the conflict situation of the maritime rules. Figure 5

[0120] Overtaking: If the unmanned ship is traveling at high speed and the angle between the heading of the unmanned ship and the obstacle is between [315°, 360°), and the distance is close to the danger distance, then the obstacle should navigate on the right side of the unmanned ship, i.e. on the left side of the unmanned ship. If the angle is between [0°, 45°] and the speed of the unmanned ship is greater than the speed of the obstacle, it is overtaking, then the left side is navigated, otherwise the right side is navigated.

[0121] Head-on meeting: If the included angle is between [165°, 195°] and the distance is close to the danger distance, the unmanned ship meets the obstacle, at which time the unmanned ship should navigate on the right side.

[0122] Crossing meeting: If the included angle is between (45°, 165°) and the distance is close to the danger distance, the obstacle meets the unmanned ship on the right side, at which time the unmanned ship should navigate on the right side. If the included angle is between (195°, 315°) and the distance is close to the danger distance, the obstacle meets the unmanned ship on the left side, at which time the unmanned ship should navigate on the left side.

[0123] Step 3: In order to avoid the unmanned ship from being trapped in a vortex when moving around the periphery of the obstacle, it is provided that when the unmanned ship moves for more than half the time, it moves in a straight line for 1 / 10 of the total time, i.e. it moves in a straight line at a constant speed for a period of time without changing the heading, and then adjusts the heading again according to the electric field distribution.​

[0124] Specifically, by Figure 6 It can be known that the unmanned ship starts from the position (100, 0), first moves uniformly along the X-axis direction, turns when moving to x=24m, and since the search area is set as the front area [L / 4, L] of the unmanned ship, the unmanned ship will not collide with the obstacle; after turning, it moves linearly according to the set trajectory, keeps straight for 1 / 10 of the time in the middle; when moving to x=-13m, the heading is adjusted, and finally moves linearly along the target position.

[0125] In order to better judge the reasons for the heading adjustment of the unmanned ship at the two inflection points, the electric field distribution when the unmanned ship moves to x=24m and x=-13m is plotted, as shown in Figure 7 and Figure 8 .

[0126] When the unmanned ship moves to x=24m, the electric field lines are arranged along the outer edge of the obstacle, and it can be judged that the motion path of the unmanned ship is distorted, and the turning occurs here; when moving to x=-13m, the electric field lines have passed through the distortion area of the obstacle, so the subsequent will move uniformly along the x direction.

[0127] The obstacle avoidance process is completed according to the distribution of the electric field lines.

[0128] Through the research of the present application, it can be determined that the method of using electric field lines for unmanned ship obstacle avoidance is feasible, although there are some rough phenomena in path selection, and the person skilled in the art knows that it is caused by the selection of the threshold value of the program in the electric field line judgment not reaching the best, and the smooth planning path can be obtained through continuous iteration optimization in the future.

[0129] It should be understood that the parts not elaborated in the specification are all prior art.

[0130] The protection scope of the present application is not limited to the above-mentioned embodiments, and obviously, those skilled in the art can make various modifications and changes to the present application without departing from the scope and spirit of the present application. If these modifications and changes belong to the scope of the claims of the present application and its equivalent technologies, the intention of the present application also includes these modifications and changes.

Claims

1. An autonomous obstacle avoidance method for an unmanned ship based on artificial electric field lines, characterized in that: Step 1: data initialization; The initialized parameters specifically include: a length L of the unmanned ship, an initial position P0 of the unmanned ship, a target position P1 of the unmanned ship movement, a radius R of the obstacle, a speed v of the obstacle movement, a heading angle θ of the obstacle movement, a movement speed v of the unmanned ship, and a heading angle θ of the unmanned ship. obs obs USV USV ​​​​ Step 2: set a safe distance range, from the position a in the forward direction of the bow of the unmanned ship, extend outward to a certain set position b, and take this range as the safe distance of the unmanned ship; Step 3: determine whether the unmanned ship has passed through several obstacles within the safe distance range; Step 4: calculate and find the minimum distance between the edge point of the obstacle within the safe distance and the bow of the unmanned ship, and obtain the obstacle closest to the unmanned ship as the priority avoidance object; Step 5: equivalent the obstacle to a circular model, calculate the change of the electric field modulus caused by the obstacle; Step 6: according to the maritime rules, judge the relative motion state between the unmanned ship and the obstacle, and make a steering selection, wherein the maritime rules include overtaking rules, head-on meeting rules, and crossing meeting rules; Step 7: according to the change of the electric field modulus, adjust the heading of the unmanned ship within the actual rudder angle change range of the unmanned ship; Step 8: update the positions and motion states of the unmanned ship and the obstacle, and re-calculate steps 1-7 until the end point is reached, completing the obstacle avoidance. In step 5, the obstacle is equivalent to a circular model, and the change of the electric field modulus caused by the obstacle is calculated, which is: the unmanned ship is regarded as a positive charge, the end position is regarded as a negative charge, and the obstacle is regarded as a sphere. The change of the electric field modulus caused by the unmanned ship and the end position outside the obstacle is calculated, and the obstacle and the unmanned ship are considered to be on the water surface.

2. The method of claim 1, wherein: In step 3, whether the unmanned ship has passed through several obstacles within the safe distance range is determined by calculating the cosine angle between the centers of the unmanned ship, the obstacle, and the end position. If the angle is acute, it is determined that the obstacle has been passed through; otherwise, it is determined that the obstacle has not been passed through.

3. The method of claim 1, wherein: In step 4, the minimum distance between the edge point of the obstacle within the safe distance and the bow of the unmanned ship is calculated, and the minimum value is found among all the calculated results. Based on the safe distance range set in step 2, the target obstacle to be avoided is determined when the minimum value is less than the safe distance.

4. The method of claim 1, wherein: In step 5, the electric field component only calculates the longitudinal component E x and the transverse component E y The calculation method of the electric field generated by a single point charge outside the sphere outside the sphere is: The charge amount of the unmanned ship is q, the charge amount of the terminal position is -q, and the distance between the unmanned ship and the sphere center of the ith obstacle is d i,USV , wherein i=1, 2…n, n is a natural number, and the radius of the ith obstacle is a i , the charge amount of the mirror charge of the unmanned ship is q' i,USV , q" i,USV , the mirror charge q' i,USV is located at a distance d' from the sphere center of the obstacle i,USV , the distance between the terminal position and the sphere center of the ith obstacle is d i,end , the charge amount of the mirror charge of the unmanned ship is q' i,end , q" i,end , the mirror charge q' i,end is located at a distance d' from the sphere center of the obstacle i,end , the mirror charge q" i,end is located at the sphere center position of the obstacle, the seawater conductivity is σ1, and the obstacle conductivity is σ2, so Wherein, k is an intermediate variable; The mirror charge related parameters of the unmanned ship are: The mirror charge related parameters of the end position are: Let the coordinates of the unmanned ship center be (x USV ,y USV ), and the horizontal component of the electric field of the unmanned ship at any position P(x, y) outside the sphere is: Let the end position be (x end ,y end ), the horizontal component of the electric field at an arbitrary position P(x,y) outside the sphere is: Let the coordinates of the ball center of the ith obstacle be (x i,obs ,y i,obs ), then the coordinates of the mirror charges q' i,USV and q" i,USV in the ith obstacle are: Let the coordinates of the ball center of the ith obstacle be (x i,obs ,y i,obs ), then the coordinates of the mirror charges q' i,end and q” i,end in the ith obstacle at the end position are: Mirror charge q' of the i-th obstacle i,USV , q" i,USV Mirror charge q' of the i-th obstacle i,end , q" i,end The horizontal component of the electric field at any position P(x, y) outside the sphere is: The horizontal component of the electric field at a point P(x, y) outside the obstacle is the linear superposition of the electric field of the drone itself with charge q, all the mirror charges q' i,USV and q" i,USV , the charge at the end position -q, all the mirror charges q' i,end , q" i,end is: The electric field modulus at a point P(x, y) outside the obstacle is: 。 5. The method of claim 1, wherein: In step 6, according to the maritime rules, the relative motion state between the unmanned ship and the obstacle is judged, and the steering selection is made, which is: The heading angle difference between the unmanned ship and the moving obstacle is described based on the heading direction of the unmanned ship, i.e. the heading angle is 0°; Overtaking: if the heading angle difference between the high-speed sailing unmanned ship and the obstacle is between [315°, 360°), and the dangerous distance is approached, the obstacle should sail on the right side of the unmanned ship, i.e. on the left side of the unmanned ship; and if the angle difference is between [0°, 45°], and the unmanned ship speed is greater than the obstacle speed, it is overtaking, then the left side is passed, otherwise the right side is passed; Head-on meeting: if the angle is between [165°, 195°], and the dangerous distance is approached, the unmanned ship meets the obstacle and collides, at this time the unmanned ship should pass on the right side; Crossing: if the included angle is between (45°, 165°) and the dangerous distance is close, the obstacle crosses the unmanned ship on the right side, at this time the unmanned ship should pass on the right side; if the included angle is between (195°, 315°) and the dangerous distance is close, the obstacle crosses the unmanned ship on the left side, at this time the unmanned ship should pass on the left side.

6. The method of claim 1, wherein: In step 7, according to the electric field x and y components, the unmanned ship heading is adjusted within the actual rudder angle change range, specifically: The electric field distribution of the unmanned ship is equivalent to five point charges, that is, the electric field distribution of the unmanned ship at a point P(x, y) outside the obstacle is superimposed by five point charges, and the five point charges are symmetrically placed at both ends of the center point of the unmanned ship with an interval of 0.25L. The forward direction of the unmanned ship is set as the search angle of the parameter c°, and the electric field Ex and Ey components at the position of -c° and c° in front of the unmanned ship are calculated when there is an obstacle or no obstacle. It is assumed that the longitudinal component of the electric field at -c° is E x0_nobs , the transverse component is E y0_nobs , the longitudinal component of the electric field at -c° is E x0_yobs , and the transverse component is E y0_yobs when there is an obstacle; it is assumed that the longitudinal component of the electric field at c° is E x1_nobs , the transverse component is E y1_nobs , the longitudinal component of the electric field at -c° is E x1_yobs , and the transverse component is E y1_yobs ; θ Δ is the angle adjustment amount, duofu is the steering direction, here it is defined that steering to the right is duofu=1, and steering to the left is duofu=-1, θ k is the heading angle at the kth moment, θ k-1 is the heading angle at the (k-1)th moment, and at the same time, according to the limitation of the actual steering angle change of the unmanned ship, if the calculated heading angle change exceeds 15°, the change is made according to 15°, and the adjustment method of the heading angle is: 。 7. The method of claim 1, wherein: In step 8, the positions and motion states of the unmanned ship and the obstacle are updated, and the calculation of steps 1-7 is performed again until the end point is reached, and the obstacle avoidance is completed; here only the position of the unmanned ship is updated, assuming that the coordinates of the unmanned ship at time k-1 before updating are (x k-1 ,y k-1 ), the speed is v k-1 , if the electric field modulus in the safety range at this time is E 0,k-1 , and if there is an obstacle, the electric field modulus is E 1,k-1 , the coordinates of the unmanned ship at time k after updating are (x k ,y k ), the speed is v k , and the heading angle is θ k , the position updating method is: 。 8. The method of claim 1, wherein: According to the actual navigation rules of unmanned vessels, the maximum change in speed, v, is limited. max It is 8 m / s. 9.A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the computer device is configured to perform the method according to any one of claims 1-8 when the computer program is executed by the processor. The processor executes the computer program to realize the unmanned ship autonomous obstacle avoidance method based on the artificial electric field line in any one of claims 1 to 8.

10. A computer-readable storage medium having stored thereon a computer program, characterized in that, The computer program is executed by the processor to realize the unmanned ship autonomous obstacle avoidance method based on the artificial electric field line in any one of claims 1 to 8.

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