A time-varying wave impedance approach for transparency compensation in bilateral teleoperation

Among the still existing issues in bilateral teleoperation, there is the inability by force-feedback control schemes to guarantee delay-independent stability and achieve both position coordination and force reflection independently of the remote environmental dynamics. Particularly, most bilateral control frameworks fail to address position coordination when interacting with rigid environments. In this paper we present a novel control strategy that aims to passively compensate for position errors that arise during contact tasks and, in general, achieve stability and transparency when alternating between unobstructed (free) and obstructed (contact) environments. The proposed control framework exploits the wave impedance independent passivity property of the scattering transformation to guarantee stability and transparency by gradually switching between a low wave impedance, ideal for free motion, and a sufficiently large impedance, suitable for contact tasks. The validity of the control framework is verified through simulations and experiments on a pair of nonlinear robots.