  Although soft robots show safer interactions with their environment than
traditional robots, soft mechanisms and actuators still have significant
potential for damage or degradation particularly during unmodeled contact. This
article introduces a feedback strategy for safe soft actuator operation during
control of a soft robot. To do so, a supervisory controller monitors actuator
state and dynamically saturates control inputs to avoid conditions that could
lead to physical damage. We prove that, under certain conditions, the
supervisory controller is stable and verifiably safe. We then demonstrate
completely onboard operation of the supervisory controller using a soft
thermally-actuated robot limb with embedded shape memory alloy (SMA) actuators
and sensing. Tests performed with the supervisor verify its theoretical
properties and show stabilization of the robot limb's pose in free space.
Finally, experiments show that our approach prevents overheating during contact
(including environmental constraints and human contact) or when infeasible
motions are commanded. This supervisory controller, and its ability to be
executed with completely onboard sensing, has the potential to make soft robot
actuators reliable enough for practical use.
