Research On Approach Of Obstacle Avoidance For Small Unmanned Surface Vessel

In recent years,with the development of unmanned technology,unmanned ships have become a research hotspot in the field of maritime navigation.The unmanned surface vessel(USV)is a kind of miniaturized unmanned ship,which has been widely used in the fields of military and civilian.The development of USV can not only expands the diversity of naval equipment,but also improves country’s protection capability of marine resources.Therefore,Deep research on USV has great significance to national defense and economic development.Collision avoidance technology is one of the key technologies of USV.The technology plays an important role in improving navigation safety.At present,many USV collision avoidance algorithms have been proposed.The global path planning algorithm has the characteristics of short path and optimal time,and has a good performance in the collision avoidance of the USV.Because of the algorithm does not consider the constraints of the USV’s motion characteristics and environmental interference.Therefore,the algorithm has the problem that the planned path is quite different from the actual trajectory of USV.The local collision avoidance algorithm has the characteristics of good accuracy and good real-time performance.Although the algorithm considers the constraint of USV’s maneuverability.However,the algorithm has the problem of excessive yaw for USV.Therefore,this paper designs a collision avoidance algorithm based on the global path planning and local collision avoidance,and builds a collision avoidance system on a 3-ton USV.The algorithm was verified by USV’s lake test.The main research contents of this paper are summarized as follows:In order to solve the problem of local optimal solution and unreachable target point of traditional path planning algorithm.This paper designs a path planning algorithm based on improved artificial potential field.According to USV route requirements,the power function of the distance change for the target point is used to improve the repulsion field model.A target point determination method based on a safe reach radius is proposed to filter dangerous target points.The method of dynamically adjusting the artificial potential field’s coefficient is used to solve the problem of local optimal solution.The simulation results show that the time for the algorithm to jump out of the local optimal solution is about 5 seconds.When there are multiple obstacles within 24.23 m radius of the target point,the USV’s path can reach the target point.In order to solve the problem that the path of traditional algorithm does not satisfy the USV’s maneuverability requirement.This paper designs a USV’s local collision avoidance algorithm based on behavior constraints.According to the USV’s motion characteristics and collision avoidance scenarios.The behavior constraint conditions of USV are constructed.The constraints satisfy the USV’s motion characteristic,dynamic obstacle avoidance,and maritime collision avoidance rules.By solving the objective optimization problem,the optimal heading and speed values of collision avoidance are calculated.Combining the above path planning and local collision avoidance algorithm,the USV’s collision avoidance scheme is proposed.The algorithm’s global path is used to constrain the local collision avoidance behavior.The method can optimize the USV’s route of resumption.The simulation results show that,when the USV’s speed is 10 knots,the USV’s safe avoidance distance is within the range of 48.45-72.68 m.The USV’s angle of avoidance is about 20 degrees.The USV’s recovery time of route is about 7 seconds.A collision avoidance system was built on the 3-ton USV.The above path planning and local collision avoidance algorithms are deployed on the 3-ton USV.The collision avoidance algorithm of USV was tested on the lake.The test results show that the collision avoidance algorithm has a short recovery time of route,and the collision avoidance behavior satisfy the USV’s maneuverability and real-time requirements.When the USV’s average speed is 10 knots,the USV’s recovery time of route is about 10 seconds.The safe avoidance distance is within the range of USV’s 6-9 times length.The USV’s angle of avoidance is about 22 degrees.The USV’s response time of collision avoidance is within the range of 2-4 seconds.