Agile and stable running locomotion control for an untethered and one-legged hopping robot

Abstract

This paper is aimed at presenting a locomotion control framework to realize agile and robust locomotion behaviors on conventional stiff-by-nature legged robots. First, a trajectory generator that is capable of characterizing angular momentum is utilized to synthesize reference CoM trajectories and associated force inputs, in accordance with the target locomotion profile. Second, the controller evaluates both force and position errors in the joint level, using a servo controller and an admittance control block. The trade-off between the position and force errors is naturally adjusted via admittance control coefficients. Implementing the controller on a 4-link, 3-jointed one-legged robot, we conducted several balancing and running experiments under challenging conditions; e.g., balancing on a moving cart, balancing on a surface with varying orientation, running on a flat surface, running on an inclined surface. The experimental study results indicated that the locomotion controller enabled the robot to perform untethered one-legged running and to maintain its balance when subject to disturbances.