基于关节构形空间的混联采摘机械臂避障路径规划

针对混联采摘机器人在非结构性环境中进行避障采摘作业的要求,该文提出了一种基于关节构形空间的混联采摘机械臂避障路径规划算法。根据机械臂和障碍物的几何特征,对机械臂及障碍物模型进行合理简化,通过分析末端执行器目标点和串联机械臂结构参数选取合适的并联机械臂动平台目标点,然后采用遍历法构建串联机械臂关节构形空间,并利用快速扩展随机树(rapidly-exploring random tree,RRT)算法搜寻串联机械臂无撞路径,再通过同样的方法获得并联机械臂关节空间障碍物映射模型和无撞路径,最后综合串、并联机械臂的无撞路径,获得混联机械臂整体的避障路径。仿真和试验结果表明,文中所提出的算法搜索的避障路径能够驱动采摘机械臂避开工作空间内的障碍物,引导末端执行器到达目标点。

Obstacle avoidance path planning of hybrid harvesting manipulator based on joint configuration space

Abstract: For the problem of obstacle avoidance fruit harvesting in unstructured environment of harvesting robot manipulator, a kind of obstacle avoidance path planning algorithm of hybrid harvesting manipulator based on joint configuration space was proposed in this paper. This paper simplified the structure of the 2P4R hybrid camellia oleifera fruit harvesting robot manipulator which is composed of a palletizing manipulator together with a spherical wrist serial manipulator, and named the link which connecting palletizing manipulator and serial manipulator as moving platform. The manipulator could accomplish six kinds of movements including waist revolution, translational motion of vertical slider and horizontal slider, and three kinds of revolute motions of the wrist part. In this paper, only five joint motions were taken into consideration, it means the last link was considered as a fix part of its previous link when collision free path planning operation was conducting, cause the motion of the last link is not related with the position of the end effector which only affect the posture of it. With the proposed algorithm, firstly select a goal point for the moving platform of the manipulator in Cartesian space which the goal point should located in the workspace of parallel manipulator and not inside the obstacles. The initial and goal configuration of the serial manipulator were determined by the goal point of moving platform, goal position of end-effector and initial posture of serial manipulator. Secondly, the obstacle mapping model in serial manipulator joint configuration space was built by using traversal method, and then attempt to search a collision-free route from initial point to goal point in this space where each point uniquely corresponding to a configuration of the serial manipulator by using rapid-exploring random tree (RRT) algorithm. Thirdly, if algorithm failed to found such a route in previous step, then repeat goal point selecting and collision-free route searching operation, otherwise built the joint configuration space of the parallel manipulator. Fourthly, determined the unique posture of parallel manipulator with the mapping relationship between driving joint value and the position coordinates of moving platform. The goal posture of parallel manipulator corresponded with a goal point in its joint space. Obstacle model was rebuilt in joint configuration space of parallel manipulator, and then reselect goal point of moving platform if the point in configuration space which corresponding to goal configuration is located in mapping model of obstacle, otherwise search a collision-free route from the start point to the goal point in configuration space which corresponding with the initial posture and goal configuration of parallel manipulator respectively by using RRT algorithm. The obstacle avoidance path of hybrid manipulator was obtained from the synthesized results of the serial manipulator and parallel manipulator collision free path. 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 of camellia oleifera fruit harvesting manipulator. The simulation and experiment results showed that the path which planned by proposed algorithm could successfully driving the end effector form initial position to the goal position without any collision, the results validated the feasibility and effectiveness of the proposed algorithm in this paper.