Impact Forces in Legged Robot Locomotion

Abstract

An energetic approach to the impact problem in planar legged robot locomotion is hereby presented. The goal is to find the configurations that yield zero tangential velocity at the impacting leg, a condition known as sticking, and restitute the least energy back into the system. With this analysis, the ground contact friction and the inertial properties of the system, including those of the servo motors, play a determinant role in the impact analysis. This approach yields an energetic criterion for the analysis of the transition from impact to contact constraint conditions. This paper presents a simple, robust method that uses the system generalized coordinates and velocities, the Jacobian, the mass matrix, the coulomb friction law, and the energetic coefficient of restitution to determine whether or not the current configuration is advantageous for maintaining contact, and thereby controllability, in the presence of impulsive forces.