Combined Modal Robust Cascade Control for Wheeled Self-Reconfigurable Robots Under Drive Failure and Safety Threat

Wheeled self-reconfigurable robots (WSRRs), a new type of multi-robot system with flexible configurations and task adaptability, have an extensive application prospects in unstructured mission environments. In this paper, based on the nonholonomic constraints and Lagrange method, the combinatorial modal kinematics and dynamics of WSRRs with arbitrary reconfiguration scale are established. At the kinematic level, based on the nonholonomic constraints, a smooth obstacle avoidance strategy based on the safety geofences is designed to ensure safety. At the dynamic level, an adaptive fault-tolerant mechanism is introduced to ensure reasonable torque distribution and avoid tracking performance degradation. Meanwhile, an improved extended state observer (IESO) is elaborated, through which the high-frequency ocsillation from measurement noises and peaking phenomenon from initial observer errors can be suppressed, and the robust velocity tracking control under unknown lumped disturbances is realized. Finally, a real-world WSRRs experiment is constructed to verify the proposed method's fault tolerance, robustness, and safety comparatively.