Foot and Body Control of Biped Robots to Walk on Irregularly Protruded Uneven Surfaces

Abstract

This correspondence proposes a control method for biped robots walking on a geometrically uneven surface with irregular protrusions. The focus is to maintain robot stability in leg and foot motions in order to adapt the foot to uneven terrains. Under the assumption that contact sensors are evenly installed at the foot soles, the geometric information under the landing foot is represented by a terrain matrix, whose elements represent the height of protruded cones. The control strategy of a landing phase (LP) is to form a large polygon with the contact points between the foot and the ground, based on the current zero-moment point (ZMP) and the locations of contact points during the transition from the LP to the stable double-support phase. The center of the polygon formed by the contact points at the end of the LP is to be used as the ZMP when the trajectory for the next step is generated. The gravity-compensated inverted-pendulum-mode-based trajectory is modified based on the newly located ZMP position and is interpolated to remove any trajectory discontinuity and to ensure a smooth transition. A series of computer simulations of a 28-degree-of-freedom (DOF) biped robot with a six-DOF environment model using SimMechanics shows that a stable compliant locomotion on uneven surfaces is successfully achieved with the proposed method.