Hybrid Soft-Rigid Actuators for Minimally Invasive Surgery.

Fluidic mechanisms have stimulated research and development in minimally invasive surgery instrumentations, because of their good performance in limited size and their force/torque generation with respect to other types of actuation systems. Fluidic solutions can be divided in two major classes: (i) elastic fluidic actuators and (ii) piston-cylinder actuators. Elastic fluidic actuators generate lower forces with smaller displacements; nevertheless, piston-cylinder solutions require seals, which can generate friction and require maintenance costs for a good reliability. The proposed solution is based on a hybrid soft-rigid actuation, which aims to overcome the limitations of both previous solutions while preserving the main advantages of the overall fluidic approach. This approach results in very compact, powerful, and low-cost actuators, which are highly customizable and adaptable to specific constraints, in medical applications but even beyond. This article proposes a novel design of hybrid soft-rigid actuators to be used as basic mechanical joints for enabling pitch and roll degrees of freedom for a miniature robotic arm. Forces up to 1.4 N and up to 2.77 N have been obtained for the above joints, respectively, and even better performance can be reached (up to 3 N) with further improvements, as demonstrated in this article.