Delicate grasping by robotic gripper with incompressible fluid-based deformable fingertips

This paper presents a gripper with fingertips constructed from incompressible fluid covered by rubber with the aim of grasping very fragile objects. Owing to the incompressibility, simply closing the gripper allows the fingertips to approach the target object with low stiffness; after contact, the contact stiffness increases with increasing fingertip deformation, and grasping with high stiffness can be realized. The adaptation of the fingertips to the object shape and a uniform contact pressure are further benefits of the proposed system. Fragile and brittle objects can be grasped by controlling the contact pressure so that it does not exceed the fracture stress/pressure. We found that the initial sign of fracture appears before total fracture when soft and ductile objects are grasped. Based on this phenomenon, we developed a strategy for grasping ductile objects without any advance knowledge of fracture. The proposed fingertips have a rigid layer inside the fluid to grasp objects with normal rigidity. The effectiveness of the fingertips was confirmed experimentally.