Reinforcement learning is a powerful technique for developing new
robot behaviors. However, typical lack of safety guarantees
constitutes a hurdle for its practical application on real robots.
To address this issue, safe reinforcement learning aims to incorporate
safety considerations, enabling faster transfer to real robots and facilitating
lifelong learning. One promising approach within safe reinforcement learning
is the use of control barrier functions. These functions provide a framework
to ensure that the system remains in a safe state during the learning process.
However, synthesizing control barrier functions is not straightforward and
often requires ample domain knowledge. This challenge motivates the exploration
of data-driven methods for automatically defining control barrier functions,
which is highly appealing. We conduct a comprehensive review of the existing
literature on safe reinforcement learning using control barrier functions.
Additionally, we investigate various techniques for automatically learning
the Control Barrier Functions, aiming to enhance the safety and efficacy
of Reinforcement Learning in practical robot applications.