Antagonistic Series Elastic Actuation for a Variable Stiffness Robotic Endoscope

Abstract

Minimally invasive neuroendoscopic procedures through the ventricular system are common to treat intraventricular pathologies. However, current rigid tools lack the maneuverability to safely access the entire ventricles. Robotic joints at the tip of the endoscope could resolve this, but unintended contacts with the brain tissue pose a safety threat. Here, we propose a bio-inspired joint actuation concept for a tendon-driven robotic endoscope for minimally invasive (neuro-)surgery. Drawing inspiration from the human musculoskeletal system, we incorporated antagonistic series elastic actuators (SEAs) to drive discrete endoscope joints. Our approach leverages the advantages of SEAs, such as mechanical compliance, faster reaction to impacts, and robust torque control. Endoscope joint stiffness can be varied during operation by continuously varying the pretension on the nonlinear springs of the actuation. We found that our prototype with two distal joints would be suitable for the expected position control maneuvers of such a neuroendoscope. Further, joint torque could be estimated with errors in the milli-Newton-meter range, deemed sufficient for detecting harmful forces. The compliant actuation absorbed external impacts, and the rise of contact forces was slower when the pretension on antagonistic tendons was decreased. While the spring design procedure needs improvement to account for friction and other transmission nonlinearities, our actuation concept holds promise for force control of tendon-driven joints. Specifically, its use in neurosurgery could provide the surgeon with increased maneuverability while ensuring a safe operation.