Journal
IEEE ACCESS
Volume 9, Issue -, Pages 145710-145727Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/ACCESS.2021.3118957
Keywords
Legged locomotion; Robots; Foot; Real-time systems; Computational modeling; Dynamics; Pallets; Legged locomotion; mobility; nonlinear model predictive control; online re-planning
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The study presents a real-time Nonlinear Model Predictive Control (NMPC) tailored to legged robots to achieve dynamic locomotion while enhancing leg mobility and terrain adaptation. Experimental results show that the NMPC is successful in traversing various terrains and obstacles.
Re-planning in legged locomotion is crucial to track the desired user velocity while adapting to the terrain and rejecting external disturbances. In this work, we propose and test in experiments a real-time Nonlinear Model Predictive Control (NMPC) tailored to a legged robot for achieving dynamic locomotion on a variety of terrains. We introduce a mobility-based criterion to define an NMPC cost that enhances the locomotion of quadruped robots while maximizing leg mobility and improves adaptation to the terrain features. Our NMPC is based on the real-time iteration scheme that allows us to re-plan online at 25 Hz with a prediction horizon of 2 seconds. We use the single rigid body dynamic model defined in the center of mass frame in order to increase the computational efficiency. In simulations, the NMPC is tested to traverse a set of pallets of different sizes, to walk into a V-shaped chimney, and to locomote over rough terrain. In real experiments, we demonstrate the effectiveness of our NMPC with the mobility feature that allowed IIT's 87 kg quadruped robot HyQ to achieve an omni-directional walk on flat terrain, to traverse a static pallet, and to adapt to a repositioned pallet during a walk.
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