Towards a Multi-imager Compatible Continuum Robot with Improved Dynamics Driven by Modular SMA

Abstract

Most existing surgical robots employ straight rigid instruments and are not compatible with imaging modalities, especially magnetic resonance imaging (MRI) that presents restrictive constraints on the robot and actuator materials. Employing continuum distal end effector and fulfilling multi-imager compatibility will potentially lead to wide adoption of surgical robots in intraoperative image-guided minimally invasive surgery (MIS). This paper introduces a 3-dimensional (3D) printed polyamide continuum robot with 2-degree of freedom, driven by modular shape memory alloy (SMA) spring actuators that enable real-time distal manipulation in 3D workspace. The multi-imager compatibility is conditionally satisfied by utilizing no ferromagnetic materials and MRI-conditional actuators in the robotic system. The use of modular SMA allows repeatable configuration setting, easy integration with active cooling strategies, and facilitates the creation of a sterile barrier between the end effector module and the actuation module. Detailed design of the robot, kinematics modeling and actuator modeling are discussed in the paper. We experimentally verified the robot kinematics and evaluated the dynamic performance of the continuum robot. It features an operating bandwidth of 0.12 Hz at -3 dB and a root-mean-square error of 0.98 mm under model predictive control when tracking sinusoidal signals, both with ±10 mm amplitude (distal bending angle of ±80^◦). As a demonstration, the robot was used as a flexible endoscope manipulator and steered under inputs from a joystick to show its real-time performance.