Compliance control for standing maintenance of humanoid robots under unknown external disturbances

For stable motions of position controlled humanoid robots, ZMP (Zero Moment Point) control is widely adopted, but needs to be integrated with other controllers due to its relatively slow response and the execution error of robots. While CoM (Center of Mass) control is much more directly than ZMP feedback control in the view of rejecting unknown external disturbance. In the meanwhile, we hope the position-based humanoid robot can have the whole body compliance in standing maintenance. So we proposes a CoM compliance controller to achieve stable standing of position controlled humanoid robot under unknown disturbance. The controller uses the concept of force control and integrates virtual model control with admittance control, where an AMPM (Angular Momentum including inverted Pendulum Model)-based virtual model with variable gain is designed to not only generate desired recovery force but also take the GRF (Grand Reaction Force) constraints into account, while an admittance controller is employed to transform the desired force to expected CoM position and body attitude. The experiments were conducted on the humanoid robot `Kong' by exerting external force disturbance and changing the slope of the ground to demonstrate the effectiveness and robustness of our method.