Aiming to realize the obstacle avoidance of fruit harvesting robot manipulator in unstructured environments, a kind of obstacle avoidance path planning algorithm of hybrid harvesting manipulator based on joint configuration space was proposed in this study. The structure of the 2P4R hybrid camellia oleifera fruit harvesting robot manipulator composed of a palletizing manipulator and a spherical wrist serial manipulator was simplified, and the link connecting the palletizing manipulator and serial manipulator was named as moving platform. The manipulator could accomplish six kinds of movements, including waist rotation, translational motions of vertical slider and horizontal slider, as well as three kinds of rotational motions of the wrist part. In this study, only five joint motions were taken into consideration. It means that the last link was considered as a fixed part of its previous link when a collision-free path planning operation was conducted. This is because that the motion of the last link was not related to the position of the end effector which could only affect its posture. Firstly, a goal point for the moving platform of the manipulator in Cartesian space was selected with the proposed algorithm. The goal point should be located in the workspace of the parallel manipulator, rather than inside the obstacles. The initial and goal configurations of the serial manipulator were determined by the moving platform of the goal point, the goal position of the end effector and the initial posture of the serial manipulator. Secondly, the obstacle mapping model in serial manipulator joint configuration space was built by using traversal method. Then, an attempt was made to search for a collision-free route from the initial point to the goal point in this space with each point uniquely corresponding to a configuration of the serial manipulator by using rapid-exploring random tree (RRT) algorithm. Thirdly, if the algorithm failed to find such a route in the previous step, the selection of goal point and collision-free route searching operation would be repeated. Otherwise, the joint configuration space of the parallel manipulator would be established. Fourthly, the unique posture of the parallel manipulator was determined based on the mapping relationship between driving joint value and the position coordinates of the moving platform. The obstacle model was built in the joint configuration space of the parallel manipulator. Subsequently, the goal point of the moving platform would be selected again, if the point in parallel manipulator configuration space corresponding to the goal configuration was located in the mapping model of obstacle. Otherwise, a collision-free route from the start point to the goal point in the configuration space corresponding to the initial posture and goal configuration of the parallel manipulator respectively should be searched by using RRT algorithm. The obstacle avoidance path of the hybrid manipulator was obtained from the synthesized results of the collision-free paths of the serial manipulator and parallel manipulator. 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. That is to say, these results can validate the feasibility and effectiveness of the proposed algorithm.%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.
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