Obstacle Avoidance Path And Trajectory Planning Of 6-DOF Manipulator

With the rapid development of science and technology,manipulator has been widely used in industry,military,aerospace and other fields.With the continuous expansion of the application scope of the manipulator,the working environment becomes more and more complex.How to make the manipulator quickly plan a collision-free path in the workspace is the focus of the manipulator path planning research.How to smooth the speed and acceleration curves of each joint during the operation of the manipulator is the focus of the research on the trajectory planning of the manipulator.The advantages and disadvantages of path planning algorithm and trajectory planning algorithm play an important role in motion control of the manipulator.This paper takes UR5 manipulator as the research object,and the main research contents are as follows:(1)Use the standard D-H method to establish the UR5 manipulator kinematics model,and complete the derivation of the manipulator's forward and inverse kinematics equations on the basis of this model.Several commonly used obstacle envelope methods are introduced in view of the obstacles existing in the working environment of the manipulator.Due to the problems of many collision detection times and complex calculation process in the collision detection between the manipulator and obstacles,this paper adopts three-layer cylinder hierarchical envelope and obstacle AABB envelope for the manipulator,This method can effectively solve the problems of many collision detection times and complex calculation process in collision detection between manipulator and obstacle.(2)Aiming at the shortcomings of the traditional RRT(Rapidly-Exploring Random Tree)algorithm that is completely random and not goal-oriented when searching for paths,an improved RRT algorithm is proposed.This algorithm combines the advantages of dual-tree expansion of dual-tree RRT algorithm and target bias of RRT algorithm,and adds virtual target and random tree variable step growth into the algorithm.Because the obstacle avoidance path searched by the improved RRT algorithm is long and has many turning points,Therefore,the strategy of two-way deletion of redundant nodes in the obstacle avoidance path and the optimal path is adopted to delete the redundant nodes in the obstacle avoidance path,and the cubic spline function is used to smooth the obstacle avoidance path after the redundant nodes are deleted.The experimental results show that the improved RRT algorithm is effective,and the removal of redundant nodes can effectively shorten the length of obstacle avoidance path.The smooth obstacle avoidance path is obtained by smoothing the cubic spline function.(3)In order to improve the stability of the manipulator in the working process,the commonly used trajectory planning methods are analyzed.Because the polynomial interpolation trajectory in the joint space is not local,and it is difficult to calculate the control points by B-spline function,the improved cubic B-spline function with auxiliary control points is used for trajectory planning.However,the acceleration curve obtained when improving the trajectory planning of the cubic B-spline function is not smooth,so the trajectory planning method of adding a correction factor to the improved cubic B-spline function is adopted.Experiments show that adding a correction factor to the improved cubic B-spline function can effectively solve the problem of unsmooth acceleration curve.(4)The UR5 manipulator simulation experiment platform is established by using ROS robot system.3D model of the UR5 manipulator is established in the simulation experiment platform,and simulation experiments and physical verification are carried out respectively.The experimental results achieve the expected results,which verifies the effectiveness of the improved algorithm and the trajectory planning method adopted in this paper.