Fin-A-Rays: Expanding Soft Gripper Compliance via Discrete Arrays of Flexible Structures

Typical soft robot grippers use a small number of "fingers," often inspired by human hands, limiting adaptability to objects. One way to increase the number of digits in the end effector is through arrays of independent flexible structures, quantizing the gripper and increasing compliance. This work investigates what happens when we "slice" a Fin Ray soft gripper into an array of discrete fingers, called Fin-A-Rays. Fin-A-Rays are modular gripper systems that can be readily integrated into an off-the-shelf two-fingered parallel gripper. Here, between one and 24 Fin Ray fingers of width 2.5 mm to 60 mm are arranged side-by-side as a gripper. An analysis of the effects of finger width on gripper stiffness and object contact is presented via finite element analysis. The design space of Fin-A-Rays was studied via experiments and simulation, and a set of performance metrics for Fin-A-Rays was defined to understand the effects of "slicing" on grasping a set of objects. A design algorithm is also introduced to prearrange a Fin-A-Ray configuration based on an image of the object. The discretized compliance across an array of fingers in a Fin-A-Ray enables several novel behaviors during grasping, including finger splay and twisting. Results show that a balance between finger widths is required when slicing Fin-A-Rays, where algorithmically designed Fin-A-Rays showed higher average performance metrics than uniform configurations. Fin-A-Rays showed new capabilities, including multiobject grasping and in-hand manipulation. The passive morphological adaptability of Fin-A-Rays simplifies grasp planning, enabling delicate grasps for picking and packing complex shapes.