  Practical use of robotic manipulators made from soft materials requires
generating and executing complex motions. We present the first approach for
generating trajectories of a thermally-actuated soft robotic manipulator. Based
on simplified approximations of the soft arm and its antagonistic shape-memory
alloy actuator coils, we justify a dynamics model of a discretized rigid
manipulator with joint torques proportional to wire temperature. Then, we
propose a method to calibrate this model from experimental data and demonstrate
that the simulation aligns well with a hardware test. Finally, we use a direct
collocation optimization with the robot's nonlinear dynamics to generate
feasible state-input trajectories from a desired reference. Three experiments
validate our approach for a single-segment robot in hardware: first using a
hand-derived reference trajectory, then with two teach-and-repeat tests. The
results show promise for both open-loop motion generation as well as for future
applications with feedback.
