  Control of soft robotic manipulators remains a challenge for designs with
advanced capabilities and novel actuation. Two significant limitations are
multi-axis, three-dimensional motion of soft bodies alongside actuator dynamics
and constraints, both of which are present in shape-memory-alloy (SMA)-powered
soft robots. This article addresses both concerns with a robust feedback
control scheme, demonstrating state tracking control for a soft robot
manipulator of this type. Our controller uses a static beam bending model to
approximate the soft limb as an LTI system, alongside a
singular-value-decomposition compensator approach to decouple the multi-axial
motion and an anti-windup element for the actuator saturation. We prove
stability and verify robustness of our controller, with robustness intended to
account for the unmodeled dynamics. Our implementation is verified in hardware
tests of a soft SMA-powered limb, showing low tracking error, with promising
results for future multi-limbed robots.
