  In this paper, we propose a novel safe, passive, and robust control law for
mechanical systems. The proposed approach addresses safety from a physical
human-robot interaction perspective, where a robot must not only stay inside a
pre-defined region, but respect velocity constraints and ensure passivity with
respect to external perturbations that may arise from a human or the
environment. The proposed control is written in closed-form, behaves well even
during singular configurations, and allows any nominal control law to be
applied inside the operating region as long as the safety requirements (e.g.,
velocity) are adhered to. The proposed method is implemented on a 6-DOF robot
to demonstrate its effectiveness during a physical human-robot interaction
task.
