We present a framework for model-free learning of event-triggered control
strategies. Event-triggered methods aim to achieve high control performance
while only closing the feedback loop when needed. This enables resource
savings, e.g., network bandwidth if control commands are sent via communication
networks, as in networked control systems. Event-triggered controllers consist
of a communication policy, determining when to communicate, and a control
policy, deciding what to communicate. It is essential to jointly optimize the
two policies since individual optimization does not necessarily yield the
overall optimal solution. To address this need for joint optimization, we
propose a novel algorithm based on hierarchical reinforcement learning. The
resulting algorithm is shown to accomplish high-performance control in line
with resource savings and scales seamlessly to nonlinear and high-dimensional
systems. The method's applicability to real-world scenarios is demonstrated
through experiments on a six degrees of freedom real-time controlled
manipulator. Further, we propose an approach towards evaluating the stability
of the learned neural network policies