Bio-inspired impedance controller and balancing feedback for the effective teleoperation of a bipedal robot

This paper presents a novel bio-inspired controller for the online tuning of the joints impedance of a humanoid robot´s arms while performing remote tele-manipulation. Emulating several behaviors observed in humans, the proposed controller accounts for the amplitude and direction of the interaction force developed at the end-effector as well as on the current arm configuration to autonomously adjust in real time the robotic arm impedance to the environmental demands. Experiments performed with the humanoid robot COMAN indicate that the proposed controller achieves a compliant behavior during collisions on the whole-arm while allowing for dexterous manipulations of different impedance environments. Additionally the integration of this local controller within the overall teleoperation framework is discussed. Of particular concern is the balance threat introduced by the impedance regulation. Indeed the joints stiffening behavior previously described allows for superior manipulation capabilities including heavy loads handling. However the large interaction forces induced may destabilize the bipedal slave. To address this concern an experimental study explores operators´ ability to rely on a cutaneous feedback of the slave´s balance state to adjust their teleoperation strategy when performing interaction tasks. Results clearly indicate that operators are able to rectify their teleoperated motions according to the vibrotactile guidance which appears thus as a mean to significantly reduce the number of falls and thus to increase the safety level.