Multi contact walking pattern generation based on model preview control of 3D COM accelerations
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 always an upward pointing cone. We reduce its computation to a convex hull of (dual) 2D points, for which optimal C(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.
2016 IEEE RAS 16th International Conference on Humanoid Robots (Humanoids)