Transparency Compensation for Bilateral Teleoperators with Time-Varying Communication Delays

Passivity-based bilateral teleoperation control systems can offer robust stability against arbitrarily large communication delays at the expense of poor transparency. In fact, most passive control frameworks are designed for a particular task and do not adjust transparency when transitioning between different environments. This paper presents a bilateral control strategy that passively compensates transparency when transitioning between free motion and hard contact motion scenarios. The proposed control framework exploits the effect that the wave impedance (a design parameter of the passivity-based scattering transformation) has on transparency without compromising closed-loop stability regardless of time-varying communication delays. To adjust transparency, the control scheme smoothly switches the wave impedance between a low value, ideal for free motion, and a sufficiently large value, suited for hard contact scenarios. We show, by rigorous mathematical treatment and simulations, that the proposed control strategy can effectively adjust the transparency of the system without compromising stability.