Integrating dynamic walking and arm impedance control for cooperative transportation

This paper presents a method for integrating a cooperative manipulation task in the design of dynamic walking motions for an underactuated bipedal robot. Applications that involve physical interaction between a walking biped and a leading human (or robot) collaborator, require that the biped exhibits compliance at the port of interaction with the collaborator, while at the same time be capable of adjusting its stepping pattern in response to the interaction forces developed. To achieve these objectives, the proposed method combines impedance control of the biped´s arm with position control of its legs in a way that the closed-loop system adapts its stepping pattern in accordance with the collaborator´s intentions. The method is applied in the case of a bipedal robot model walking over flat ground and up and down stairs of known geometry under the influence of a trajectory that is unknown to the biped and represents the intention of a collaborator.