Objective  In order to solve the problems of poor training efficiency and low success rate of picking path planning of manipulator using deep reinforcement learning (DRL), this study proposed a path planning method combined with DRL and artificial potential field for citrus picking manipulator in unstructured environments.

Method  Firstly, the picking path planning problem was solved by the DRL with artificial potential field method. Secondly, the longshort term memory (LSTM) structure was introduced to improve the Actor network and Critic network of two DRL algorithms. Finally, the DRL algorithms were trained in three different unstructured citrus growing environments to perform path planning for picking manipulator.

Result  The comparison of simulation experiments showed that the success rate of path planning was effectively improved by combining DRL with the artificial potential field method, the method with LSTM structure improved the convergence speed of the deep deterministic policy gradient (DDPG) algorithm by 57.25% and the success rate of path planning by 23.00%. Meanwhile, the method improved the convergence speed of the soft actor critic (SAC) algorithm by 53.73% and the path planning success rate by 9.00%. Compared with the traditional algorithm RRT-connect (Rapidly exploring random trees connect), the SAC algorithm with LSTM structure shortened the planned path length by 16.20% and improved the path planning success rate by 9.67%.

Conclusion  The proposed path planning method has certain advantages for path planning length and path planning success rate, which can provide references for solving path planning problems of picking robots in unstructured environments.