Safe Reinforcement Learning for Legged Locomotion

Jimmy Yang
Peter J. Ramadge
Sehoon Ha
International Conference on Robotics and Automation(2022) (to appear)
Google Scholar


Designing control policies for legged locomotion is complex due to underactuation and discrete contact dynamics. To deal with this complexity, applying reinforcement learning to learn a control policy in the real world is a promising approach. However, safety is a bottleneck when robots need to learn in the real world. In this paper, we propose a safe reinforcement learning framework that switches between a safe recovery policy and a learner policy. The safe recovery policy takes over the control when the learner policy violates safety constraints, and hands over the control back when there are no future safety violations. We design the safe recovery policy so that it ensures safety of legged locomotion while minimally interfering with the learning process. Furthermore, we theoretically analyze the proposed framework and provide an upper bound on the task performance. We verify the proposed framework in three locomotion tasks on a simulated quadrupedal robot: catwalk, two-leg balance, and pacing. On average, our method achieves 48.6% fewer falls and comparable or better rewards than the baseline methods.