Research On Multi-UAV Cooperative Obstacle Avoidance Method In Dynamic Environment

With the development of the times,multi-UAV systems have been widely used in various military and civilian environments and many dangerous missions,resulting in crowded low-altitude areas year by year and frequent UAV collision events.The safety of UAVs has aroused widespread concern in scientific research institutes.One of the core points of the obstacle avoidance problem is the obstacle avoidance algorithm.This thesis studies the obstacle avoidance problem of multiple UAVs in view of the situation of multiple UAVs performing tasks cooperatively.The main content has the following three aspects:（1）Analyze the multi-UAV obstacle avoidance problem,and divide the obstacle avoidance problem into two levels according to the needs of multi-UAV obstacle avoidance and whether the obstacles are predicted in advance.One is the global path planning of known obstacles,and the other is Dynamic obstacle avoidance with detection of obstacles through UAV communication and sensors.Aiming at the problem of multi-UAV communication,two common communication protocols are compared,and due to the high communication efficiency of User Datagram Protocol（UDP）,which is more in line with the requirements of dynamic obstacle avoidance,UDP is used for multi-UAV communication.（2）For static obstacles known in advance,an improved RRT algorithm is used for global path planning.In this thesis,in order to improve the efficiency of the UAV search path,the KD tree nearest neighbor search method is added to find the nearest point.In order to reduce unnecessary inflection points of the UAV path,a greedy algorithm is used to "prune" the path to shorten the path length.In order to smooth the path,a cubic B-spline is used to make the path more consistent with the dynamic characteristics of the UAV’s speed,acceleration,and angular velocity continuity.At the same time,in order to prove the effectiveness of the global path planning algorithm,a simulation comparison experiment is carried out.（3）Obstacle avoidance for UAV dynamic environment.Firstly,a dynamic environment model is established,and then for UDP communication,an information update algorithm is proposed to reduce information redundancy and update the stored information.Secondly,based on the proposed communication algorithm and using the improved Velocity Obstacle（VO）method for dynamic obstacle avoidance,when it is determined that the distance between the UAVs is less than the obstacle avoidance distance,the obstacle avoidance judgment is performed.If it is judged that there is no collision,the current state is maintained.otherwise,the improved VO method is used to avoid obstacles,and the global path is restored after the threat is removed.Finally,when encountering unknown static rules and irregular static obstacles,the improved VO method is also used to avoid obstacles according to the coordinates of the obstacles measured by the carried sensors.Finally,by restoring the urban environment and the complex multi-wall environment in GAZEBO and simulating,it is verified that the global path planning algorithm and the local dynamic obstacle avoidance algorithm have high obstacle avoidance efficiency in the actual environment and can generate better obstacle avoidance paths.