Inertia-coupling based balance control of a humanoid robot on unstable ground

A humanoid robot should be able to keep balance in the presence of various disturbances. We address here a class of disturbances that are due to an unstable ground, when conventional methods of control, e.g. ZMP based ones, are not applicable. The equation of motion has the form of an underactuated system, such as that of a free-flying robot or of a flexible-base/flexible-link robot. We develop an inertia-coupling based control method, similar to the control methods used in previous works for vibration suppression of flexible-base robots. Simulations with a planar humanoid robot are presented for two types of disturbances: (i) rotating surface and (ii) jointed-toe foot model. It is shown that, under the proposed control laws, balance can be recovered in a stable and optimal way, in both cases.