  In this paper, we present a controller that combines motion generation and
control in one loop, to endow robots with reactivity and safety. In particular,
we propose a control approach that enables to follow the motion plan of a first
order Dynamical System (DS) with a variable stiffness profile, in a closed loop
configuration where the controller is always aware of the current robot state.
This allows the robot to follow a desired path with an interactive behavior
dictated by the desired stiffness. We also present two solutions to enable a
robot to follow the desired velocity profile, in a manner similar to trajectory
tracking controllers, while maintaining the closed-loop configuration.
Additionally, we exploit the concept of energy tanks in order to guarantee the
passivity during interactions with the environment, as well as the asymptotic
stability in free motion, of our closed-loop system. The developed approach is
evaluated extensively in simulation, as well as in real robot experiments, in
terms of performance and safety both in free motion and during the execution of
physical interaction tasks.
