Tele-manipulation with a humanoid robot under autonomous joint impedance regulation and vibrotactile balancing feedback

This work presents an enriched human-machine interface for performing effective tele-manipulation using a humanoid robot. To provide the slave with the ability to dexterously interact with the remote environment, we implement an autonomous impedance controller that regulates the slave's joints stiffness and damping according to the manipulation loading conditions. In the proposed strategy, free-space operations are performed with compliant limbs to ensure safe interactions during unforeseen collisions on the whole-arm together with a soft behaviour at the initial phase of contact. During the manipulation task, the designed controller accounts for the arm configuration and the direction/amplitude of the external force sensed at the end-effector to stiffen the humanoid arm joints, permitting to handle the task loads. Experiments performed on the compliant humanoid robot COMAN demonstrate the effectiveness of this human-inspired impedance controller during a teleoperated pick-and-place task. The interaction forces during manipulation can destabilize the floating base humanoid robot. To address this concern we also investigate the operators ability to rely on a cutaneous feedback of the slave's balance state to adjust their teleoperation strategy when required so as to complete the task while maintaining the slave's balance. A comparative study shows that the proposed vibrotactile feedback allows for a proper recognition of the slave's drop of stability during interaction tasks and that the tactile guidance leads to enhanced teleoperation performances characterized by a significantly lower number of falls.