Computation of Regions of Attraction for Hybrid Limit Cycles Using Reachability: An Application to Walking Robots
This work addresses stability analysis for hybrid robotic systems like legged robots, which is incremental as it extends existing reachability tools to handle state resets.
The authors tackled the problem of computing regions of attraction for hybrid limit cycles in contact-rich robotic systems, such as walking robots, by generalizing the Hamilton-Jacobi reachability framework to handle discontinuous state changes from state resets, resulting in a method that recovers a bigger region-of-attraction than state-of-the-art approaches.
Contact-rich robotic systems, such as legged robots and manipulators, are often represented as hybrid systems. However, the stability analysis and region-of-attraction computation for these systems are often challenging because of the discontinuous state changes upon contact (also referred to as state resets). In this work, we cast the computation of region-ofattraction as a Hamilton-Jacobi (HJ) reachability problem. This enables us to leverage HJ reachability tools that are compatible with general nonlinear system dynamics, and can formally deal with state and input constraints as well as bounded disturbances. Our main contribution is the generalization of HJ reachability framework to account for the discontinuous state changes originating from state resets, which has remained a challenge until now. We apply our approach for computing region-of-attractions for several underactuated walking robots and demonstrate that the proposed approach can (a) recover a bigger region-of-attraction than state-of-the-art approaches, (b) handle state resets, nonlinear dynamics, external disturbances, and input constraints, and (c) also provides a stabilizing controller for the system that can leverage the state resets for enhancing system stability.