The SCF-EM Gripper: Using Sleeved Concentric-Flexures Eversion Mechanisms as Fingers for Confined-Space Robotic Grasping

Abstract

Abstract. This article presents the specially developed sleeved concentric-flexure eversion mechanism (SCF-EM) gripper, which employs specially developed SCF-EM as fingers for grasping in confined spaces, with a focus on food handling applications. The gripper minimizes environmental disturbance by moving its fingers tangentially along an object’s surface while setting the grasp, in contrast to conventional grippers that approach perpendicularly. Each SCF-EM finger features an eversion sleeve actuated by two concentrically placed precurved flexures between its inner and outer sides, synchronized via a cable–pulley system. This constitutes as a mechanically actuated eversion mechanism–driven not by pneumatic pressure, as in traditional designs, but by advancing an internal flexure from its base to push against the sleeve interior. A prototype gripper, equipped with three SCF-EM fingers, was manufactured for grasping tomatoes piled in a crate. To evaluate its performance, three key metrics were defined and experimentally validated. The results show (1) a 100% grasp success rate for the specified task, demonstrated on a robotic test setup, (2) low induced disturbance forces—1.7 N normal and 1.5 N tangential—sufficiently gentle to avoid product damage, and (3) a 10.0 N pull-out force, ample for lifting tomatoes, corresponding to 4–10× their weight. These results demonstrate the SCF-EM gripper’s effectiveness for delicate object handling in confined environments and highlight the potential of mechanically driven eversion mechanisms.