Robust higher order sliding mode based impedance control for dual-user teleoperation under unknown constant time delay

This paper presents a dual-user teleoperation scheme to perform a collaborative task using n-DOF nonlinear manipulators as masters and slave. It consists on impedance controllers for the manipulators in order to achieve a desired dynamic behavior depending on the user's necessities. Moreover, to cope with the uncertainty in the slave, a sliding mode controller is introduced and a desired impedance model for the salve is chosen as the sliding surface. Since the slave teleoperator is in contact with a rigid environment, the slave controller requires a free of chattering control strategy, which makes first order sliding mode teleoperation control unsuitable. Then a higher order sliding mode based impedance controller is proposed to guarantee robust impedance tracking under constant, but unknown time delay. Therefore, a position scaling factor is incorporated to deal with the different workspaces among masters and slave. The validity of the proposed control scheme is demonstrated via simulations performed on a 3-DOF dual-user teleoperation system. The simulation setup includes a Phantom Premium 1.0, a Phantom Omni, a Catalyst-5 and communication channels which suffer from constant unknown time delays.