Selectively Tunable Joints With Variable Stiffness for a Magnetically-Steerable 6-DOF Manipulator

Abstract

Robotic manipulators are used across various surgical tasks, including endoscopic and laparoscopic procedures. Operating in small and constrained spaces during these procedures requires the manipulators to have high dexterity and control over the motion path but with a small footprint. In this work, we propose a modular design of a magnetically-guided small-sized robotic manipulator. The manipulator has discrete universal joints that allow ease of actuation. Variable stiffness is incorporated into the joints to allow the locking and unlocking of individual degrees of freedom (DOFs). The design is modular and allows extension to additional DOFs. The range of each DOF is 60° and is controlled by a pair of shape memory polymer flexures; four flexures comprise one joint. With rolling-contact elements, the design eliminates problems with buckling and pushability. A custom-designed heating element triggers the flexures to switch from a high (0.57Nmm/°) to a low stiffness (0.06Nmm/°) state within 14(±0.8)s. Ambient cooling secures shape-locking within 64(±3.7)s. In an experiment, a 6-DOF version of the manipulator navigates around obstacles in confined spaces and remains shape-locked for stable operation. Practical application is demonstrated through simulated gastroscopy and polypectomy using inserted surgical tools.