A sliding controller for bipedal balancing using integrated movement of contact and non-contact limbs

We present an algorithm that provides enhanced flexibility and robustness in the control of single-leg humanoid standing through the coordination of stance leg ankle torques and stabilizing movements of non-contact limbs. Current control approaches generally assume the presence of explicitly specified joint reference trajectories or desired virtual force calculations that ignore system dynamics. Here we describe a practical controller that 1) simplifies control of abstract variables such as the center of mass location using a two-stage model-based plant linearization; 2) determines motion of non-contact limbs useful for achieving control targets while satisfying dynamic balance constraints; and 3) provides robustness to modeling error using a sliding controller. The controller is tested with a morphologically realistic, 3-dimensional, 18 degree-of-freedom humanoid model serving as the plant. It is demonstrated that the controller can use less detailed control targets, and reject stronger disturbances, than previously implemented controllers that employ desired virtual forces and static body calculations.