Towards real-time SMA control for a neurosurgical robot: MINIR-II

Abstract

Intraoperative magnetic resonance image (MRI)-guided neurosurgical procedure is receiving much attention due to the use of real-time image feedback instead of pre-operative images when resecting the tumor. We envision a real-time MR image-guided robotic neurosurgery that utilizes a dexterous meso-scale surgical robot that can work in tight spaces. In this work, we introduce an MR-compatible robotic platform for a spring-based prototype of the minimally invasive neurosurgical intracranial robot (MINIR-II). The robot consists of an outer spring and an inner interconnected spring that has three segments, each of which has two degrees of freedom (DoFs). Each joint of the robot is actuated by an antagonistic pair of shape memory alloy (SMA) spring actuators with integrated water cooling modules. The proposed water-based cooling strategy is designed to improve the cooling rate and thus the actuation bandwidth of SMA springs so that the neurosurgical robot can be operated at sufficiently high bandwidth. We characterized our cooling module integrated SMA springs based on several parameters including the current supplied, water flow rate, SMA pre-strain, gauge pressure of the compressed air, and motion amplitude. We developed a vision-based experimental setup to perform the characterization experiments and optimized the actuator performance in terms of its actuation bandwidth. We commanded the base and middle segments of the robot to follow a series of step input references to verify the improved actuation bandwidth of the antagonistic SMAs. Finally, we performed experiments to allow continuous and coordinated motion between the base and middle segments to verify the robot’s independent joint controllability and motion repeatability.