  Within the framework of Sliding Mode Control, safety critical control looks
at two problems of theoretical significance: construct a sliding manifold that
does not intersect a given unsafe set of the state space, and design a robust
controller that safely takes the system trajectory to the manifold during the
reaching phase and enforces the sliding motion. In this technical note, we
address both problems. We introduce the notion of Safe Sliding Manifold (SSM)
of relative degree one, and show that it is possible to construct it from the
gradient of a class of Lyapunov-like energy functions, previously reported in
the literature, used to asses stability and safety of a nominal system. The
constructed SSM allows us providing a robust safe controller for a fair general
class of uncertain nonlinear systems.
