Motion planning for the discretely actuated steerable cannula

Discretely actuated steerable cannula is a multi-degree-of-freedom probe that could potentially be used to deliver therapeutic and diagnostic tools to the appropriate location through its hollow inner core. The cannula is composed of straight segments connected by shape memory alloy actuators (SMA) that generate local bending at discrete locations along the probe length. We take advantage of the redundancy of the cannula and apply configuration control approach to develop motion planning algorithms to steer the cannula to a desired location while avoiding obstacles. The maximum bending angle that can be achieved by the SMA actuator depends on the physical and mechanical properties of the SMA actuator, the initial strain of the SMA before actuation and the mechanical properties of the soft-tissue. Hence, we also investigate the maximum bending angle that can be achieved in motion planning. We demonstrate that the planner can successfully find trajectories in the presence of moving obstacles while avoiding the joint limits. Therefore, the planner can be used to steer the cannula under image guidance.