Fingerless Soft Gripper Capable of Omnidirectional Deformations: Proof-Of-Concept

Fingerless soft grippers have shown a strong potential in effectively engaging objects regardless grasping postures and prior knowledge of the objects. Nonetheless, ensuring both the number of contacts and adequate aperture diameters remains as open challenge. To address these issues, this work presents a novel fingerless soft gripper capable of stable grasping via omnidirectional deformation, utilizing strain-induced structural mechanics of pleats. The gripping motions are based on a cylindrical tube type air chamber with a pleated pattern on the inner wall and a smooth outer wall, which produces bidirectional deformations upon negative and positive pressures. More specifically, at the inflation phase, the aperture diameter increases, resulting in the release of the object. Conversely, the aperture diameter decreases upon positive pressure, allowing for the engagement of the object, similar to a form closure type gripper. In this paper, a comparison study is conducted to investigate different morphological and geometrical features of the gripper. As a result, their mechanical characteristics (i.e., deformation in radial direction, equivalent strain, etc.) are quantitatively analyzed. The results provide insights with a design strategy for developing fingerless soft gripper with convoluted patterns and asymmetric membrane thickness.