Foot Pressure Control Based on Extraction of Environment Mode

In walking motion of biped robots, Zero Moment Point (ZMP) is treated as important. ZMP is a stability index and keeping ZMP in the stable region is important for biped robots to walk. In this paper, foot pressure control based on extraction of environment mode is proposed as a ZMP stabilizing control. Environment mode is representation of connection between the robot and the environment. In this control, the reaction force acting on the sole from the ground are extracted as environment mode. By controlling foot pressure according to environment mode, ZMP is kept in the stable region. Conventional mode control is not able to be applied to the movement of desired ZMP. However, the proposed control is able to deal with the movement by generating mode command from ZMP reference trajectory, which is desired ZMP trajectory. The error between mode command and mode response is suppressed by mode compliance control. The validity of the proposed method is confirmed by simulations and experiments. In human walking motion, ZMP moves from heel to tip in single support phase. With the proposed environment mode control, the robot is able to walk stably adapting such a ZMP reference trajectory.