Research On Obstacle Avoidance Algorithm Of Harvesting Robot Manipulator Using Sampling Based Method

The application of harvesting robot in agriculture is helpful to alleviate the problem of shortage of agricultural labor force,and can greatly improve the market competitiveness of agricultural products.However,the application and development of harvesting robot is seriously restricted by the problem of obstacle avoidance path planning in workspace.Therefore,research on obstacle avoidance path planning for harvesting manipulator has important practical significance and wide application prospects.This paper studies from three aspects:fast configuration space construction algorithm,construction of manipulator collision detection model,collision-free path planning algorithm for high dimensional space.Advantages and disadvantages of the existing obstacle avoidance path planning algorithm are analyzed,and then configuration space is selected as the path planning space in this paper.The weakness of the traditional configuration space is introduced,and then a two phase fast configuration space construction algorithm is proposed which consists of an off-line and an on-line phase.In the off-line phase of the algorithm,the obstacle collision query database(OCQD)and the self-collision query database(SCQD)are constructed by iterating all the configurations of manipulator.In the online phase,cells that occupied by the obstacles in real-time scenario are calculated,and then OCQD and SCQD that constructed in off-line phase are indexed by the serial number of the occupied cells in workspace.Based on the analysis of the weakness of common collision detection technology and spatial bounding box,the oriented bounding box is selected as the fitting model of the manipulator.Local coordinate system is constructed by using geometrical analysis method and space vector method,and then the local coordinate system is attached on the oriented bounding box to represent the vertex coordinates of the box.Homogeneous transformation matrix between local coordinate system and world coordinate system is established,which could transform the coordinates of the box vertex represented in local coordinate system into world frame.A detailed analysis and research is carried out on the typical path planning algorithm as graph based,heuristic based,sampling based and intelligent algorithm.Considering the dimension of configuration space in this study,the sampling based algorithm is selected as the path planning method.The bidirectional rapidly-exploring random tree(RRT-Connect)algorithm and asymptotically optimal rapidly-exploring random tree(RRT*)are merged and result a kind of algorithm which not only inherited the advantage of speed performance from RRT-Connect,but also retain the optimal feature of the RRT*.In order to verify the feasibility and effectiveness of the proposed algorithm,the path planning simulation of a hybrid manipulator in Matlab was carried out.The proposed algorithm was also applied in the obstacle avoidance path planning experiment on the camellia oleifera fruit harvesting manipulator.According to the simulation and experiment results,the path planned by the proposed algorithm could successfully drive the end effector from its initial position to the goal position without any collision.