A dynamic model for the active catheter actuated by the shape memory alloy coil spring

This paper focuses on the transient behavior of a simple active catheter composed of a bias stainless steel spring and a one-way SMA coil spring. We combine the bending mechanics derived using a circular arc model, the SMA actuator characteristic described by Liang's model, and a heat transfer model to form the dynamics of the catheter. The phase transformation condition is modified according to whether there is overlapping between two phase transform bands. The response of derived dynamic model is simulated and verified for both complete and incomplete phase transformation. A self-tuning fuzzy PID controller is also designed to be used for such a SMA structure, which exhibits effective performance through simulations.