Loop closure grasping: Topological transformations enable strong, gentle, and versatile grasps

TL;DR

The mechanisms’ initial open-loop topology enables versatile grasp creation via unencumbered tip movement, and closing the loop enables strong and gentle holding with effectively infinite bending compliance.

Abstract

Grasping mechanisms must both create and subsequently hold grasps that permit safe and effective object manipulation. Existing mechanisms address the different functional requirements of grasp creation and grasp holding using a single morphology, but have yet to achieve the simultaneous strength, gentleness, and versatility needed for many applications. We present "loop closure grasping", a class of robotic grasping that addresses these different functional requirements through topological transformations between open-loop and closed-loop morphologies. We formalize these morphologies for grasping, formulate the loop closure grasping method, and present principles and a design architecture that we implement using soft growing inflated beams, winches, and clamps. The mechanisms' initial open-loop topology enables versatile grasp creation via unencumbered tip movement, and closing the loop enables strong and gentle holding with effectively infinite bending compliance. Loop closure grasping circumvents the tradeoffs of single-morphology designs, enabling grasps involving historically challenging objects, environments, and configurations.

Figures (11)

• Figure 1: An overview of loop closure grasping. The grasping process can be decomposed into two stages, grasp creation and grasp holding, connected by topological transformation. (A) Grasping mechanisms with open-loop topologies are advantageous for versatile grasp creation, as illustrated by biological open-loop grasping mechanisms. (B) Grasping mechanisms with closed-loop topologies are advantageous for strong and gentle grasp holding, as illustrated by examples of closed-loop grasping mechanisms. (C) Loop closure grasping process. Topological transformations enable mechanisms to transition their morphology from open-loop to closed-loop. By transforming its topology from open-loop to closed-loop between the grasp creation and holding stages, a grasping mechanism can leverage the advantages of the right topology at the right stage. (D) A loop closure grasping system prototype grasping and lifting a glass vase. Scale bars, 5 cm. (A) Photo Credit: Leung Cho Pan, Alamy Ltd.; Photo Credit: oboltus, iStockphoto LP. (B) Photo Credit: tonobalaguer, Inmagine Lab Pte Ltd; Photo Credit: N/A, SureHands® Lift & Care Systems. Note that we have the licenses for, or permission to use these images and are entitled to use these materials by their associated owners.
• Figure 2: Topological model of grasping mechanisms and the loop closure grasping method.(A-B) Defining components and features of an open-loop and a closed-loop grasping mechanism, respectively. $c$ denotes a contact point. (C) Formal loop closure grasping method, sequenced in its three steps: open-loop grasp creation, topological transformation, and closed-loop grasp holding. (D) Pressure distributions between a circular object and five different closed-loop mechanisms with different flexural rigidities.
• Figure 3: Loop closure grasping system design architecture and components design.(A) System design architecture with components labeled. (B) Robotic implementation using soft growing inflated beams (i.e., vine robots), clamps, and winches. Our implementations of these mechanisms satisfy the design principles for each component and the overall architecture to enable and realize the loop closure grasping method. (C) Component designs for our large-scale and small-scale sets of system modules. Theoretical load capacity limits of the system due to vine robot material yielding, and the retraction force limits and fastening load capacities of the base and the tip.
• Figure 4: Grasp versatility demonstrations.(A) Weaving around an object to secure it (B) Creating Hopf link by interlocking with ring (C) “In hand” manipulation of a grasped object. (D) Grasping object in a cluttered environment (E) Grasping an object rested 3 m away from grasping mechanism.
• Figure 5: Harnessing and lifting demonstrations.(A) Harnessing and lifting a human subject with large-scale grasping implementation system. (B) Simultaneously grasping and transferring multiple objects. (C) Grasping and transferring a heavy yet fragile object (watermelon).