  In bilateral teleoperation, the human who operates the master and the
environment which interacts with the slave are part of the force feedback loop.
Yet, both have time-varying and unpredictable dynamics and are challenging to
model. A conventional strategy for sidestepping the demand for their models in
the stability analysis is to assume passive user and environment, and to
control the master-communications-slave system to be passive as well. This
paper circumvents the need to model the user and environment in a novel way: it
regards their forces as external excitations for a semi-autonomous force
feedback loop, which it outfits with a dynamic interconnection and damping
injection controller that renders bilateral teleoperation with time-varying
delays exponentially input-to-state stable. The controller uses the position
and velocity measurements of the local robot and the delayed position
transmitted from the other robot to robustly synchronize the master and slave
under the user and environment perturbations. Lyapunov-Krasovskii stability
analysis shows that the proposed strategy (i) can confine the position error
between the master and slave to an invariant set, and (ii) can drive it
exponentially to a globally attractive set. Thus, the dynamic interconnection
and damping injection approach has practical relevance for telemanipulation
tasks with given precision requirements.
