Towards high frequency actuation of SMA spring for the neurosurgical robot - MINIR-II

Robotic surgery, especially in the field of neurosurgery, can be tremendously improved with the integration of an excellent imaging modality during the procedure. Shape memory alloy (SMA), a high power density and inexpensive MRI-compatible actuator, is therefore being considered as an appropriate actuator for the robot. However, the low control bandwidth of SMA due to the long cooling time makes it undesirable for commercial use. An efficient and low-cost cooling method using water as a coolant that passes through a flexible tube coiled around the SMA spring is proposed to increase the cooling rate of SMA, thereby improving its actuation frequency. SMA constitutive model and heat transfer model have been developed to simulate theoretical behavior of SMA springs in antagonistic configuration. The maximum bandwidth we achieved was 0.333 Hz for tracking of a sinusoidal trajectory of 3 mm peak-to-peak magnitude. We also demonstrated the capability of our cooling system to control the motion of an SMA spring actuated one-DOF MINIR-II robot prototype.