Multi-contact Walking Pattern Generation based on Model Preview Control of 3D COM Accelerations
This work addresses the challenge of dynamic stability for humanoid robots in complex environments, representing an incremental improvement in computational efficiency for multi-contact walking.
The authors tackled the problem of generating stable walking patterns for humanoid robots in multi-contact scenarios by developing a pattern generator based on preview-control of 3D center of mass accelerations, resulting in a significant speedup in computing contact-stability constraints using an O(n log n) algorithm and enabling real-time control.
We present a multi-contact walking pattern generator based on preview-control of the 3D acceleration of the center of mass (COM). A key point in the design of our algorithm is the calculation of contact-stability constraints. Thanks to a mathematical observation on the algebraic nature of the frictional wrench cone, we show that the 3D volume of feasible COM accelerations is a always a downward-pointing cone. We reduce its computation to a convex hull of (dual) 2D points, for which optimal O(n log n) algorithms are readily available. This reformulation brings a significant speedup compared to previous methods, which allows us to compute time-varying contact-stability criteria fast enough for the control loop. Next, we propose a conservative trajectory-wide contact-stability criterion, which can be derived from COM-acceleration volumes at marginal cost and directly applied in a model-predictive controller. We finally implement this pipeline and exemplify it with the HRP-4 humanoid model in multi-contact dynamically walking scenarios.