Abstract: Real-time collision avoidance in dynamic environments is a challenge in trajectory planning of mobile robots. Focusing on environments with variable number of obstacles,this paper proposes a real-time trajectory planning algorithm,Crit-LSTM-DRL,based on long short-term memory(LSTM) and deep reinforcement learning(DRL). First,it predicts the time to the occurrence of a collision between an obstacle and the robot based on their states,and then computes the collision criticality of each obstacle with respect to the robot. Second,it generates the obstacle sequence based on the collision criticality and abstracts a fixed-dimension vector by LSTM to represent the environment. Finally,the robot state and the extracted vector are concatenated as the input of the DRL's value network to compute the value with respect to the system state. At any instant,for each action,it predicts the value of the next state based on the LSTM and DRL models and then the value of the current state; hence,the action generating the maximal value of the current state is selected to control the robot. To evaluate the performance of Crit-LSTM-DRL,it is first trained in three different environments and obtain three models: the model trained in the environment with 5 obstacles,the model trained in the environment with 10 obstacles,and the model trained in the environment with variable number of obstacles(1～10). The models then are tested in various environments containing different number of obstacles. To further investigate the effects of the interaction between an obstacle and the robot,this paper also takes the joint state of an obstacle and the robot as the state of the obstacle and trains another three models in the above training environments. Experimental results show the effectiveness and efficiency of Crit-LSTM-DRL.

Key words: Trajectory planning, Collision avoidance, Obstacle criticality, Deep reinforcement learning