Eversion-capable Fabric Robot Gripper with Novel Retraction Mechanism

Soft grippers have a number of advantages over their conventional stiff-bodied counterparts; not only do they surpass them in ease of fabrication and safety but also, in many cases, require less complex control strategies - due to natural compliance and form-fitting plasticity. Pneumatically actuated soft grippers made from non-extensible fabrics or polyethylene sheets have been shown to outperform soft silicone grippers capable of applying greater forces to the environment. Despite progress in the field, grasping a given object within a confined space proves challenging for both soft and conventional robotic grippers. A key issue is that most grippers use rotary or lateral translational motion when grasping an object, hence other objects in the scene may impede the closing motion as the gripper attempts to reach the target. In this study, we present a novel design for a soft robotic gripper equipped with a brace of fabric-based fingers capable, by way of eversion, of longitudinal extension, bending, and retraction, i.e. returning to a stowed state. Our experiments show that from the retracted to fully-extended state, the gripper fingers extend by up to 200% in length. To test the performance of the design, force characterisation experiments and grasping operations were carried out, demonstrating that each finger is capable of as much as 30 N of maximum tip force and can bend to an angle of 127 degrees. At a bending pressure of 82.7 kPa (the maximum tested pressure in the bending chamber), a maximum (pullout) force of 16 N is needed to release an object that has been grasped by the finger. The experimental scenario detailed features all three mechanisms (eversion, bending and retraction) discussed.