Torsion Resistant Strain Limiting Layers Enable High Grip Strength of Electrically-Driven Handed Shearing Auxetic Grippers

Torsion Resistant Strain Limiting Layers Enable High Grip Strength of Electrically-Driven Handed Shearing Auxetic Grippers Ian Good, Srivatsan Balaji, and Jeffrey I. Lipton Abstract --Soft grippers have demonstrated a strong ability to successfully pick and manipulate many objects. A key limitation to their wider adoption is their inability to grasp larger payloads due to objects slipping out of grasps. We have overcome this limitation by introducing a torsionally rigid strain limiting layer (TR-SLL). This reduces out-of-plane bending while maintaining the gripper's softness and in-plane flexibility. We characterize the design space of the strain limiting layer and Handed Shearing Auxetic (HSA) actuators for a soft gripper using simulation and experiment. The inclusion of the TR-SLL with HSAs enables HSA grippers to be made with a single digit. We found that the use of our TR-SLL HSA gripper enabled pinch grasping of payloads over 1 kg. We demonstrate a lifting capacity of 5 kg when loading using the TR-SLL. We also demonstrate a peak pinch grasp force of 5.8 N, and a peak planar caging force of 14.5 N. Finally, we test the TR-SLL gripper on a suite of 43 YCB objects. We show success on 37 objects demonstrating significant capabilities. I NTRODUCTION Soft robotic fingers have focused on emulating the ability of human and other biotas compliance when bending [1]. However, the key to human's remarkable grip is that our fingers can simultaneously bend while resisting torsion and lateral loading. People rely on a rigid skeleton with discrete joints to provide this selective compliance. We build upon a previous conference paper that introduced the torsion resistant strain limiting layer (TR-SLL) [2]. The TR-SLL provides soft grippers with same torsion resistance of a skeleton without discretization. This work extends this to entirely electrically driven grippers. This allows a single Handed Shearing Auxetic (HSA) to be used in gripper and produce a high holding force. The TR-SLLs constrict bending and serves as a reaction body for the HSA.