Delicate Food Grasping by Robotic Gripper with Viscoelastic Fluid-based Deformable Fingertips

This paper presents a robotic gripper with fingertips constructed from viscoelastic fluid covered by rubber with the aim of grasping very fragile foods. The viscoelastic fluid has incompressibility providing several merits. The gripper just has to close. The fingertips can 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 other merits are the adaptation to the object shape and a uniform contact pressure. Fragile and brittle objects can be grasped by controlling the contact pressure so that it can be under the fracture pressure/stress. When soft and ductile objects were grasped, a phenomenon appeared before total fracture; contact pressure keeps constant irrespective the penetration of fingertip. Utilizing this phenomenon, a strategy for grasping ductile objects without any advance knowledge of fracture is presented. The developed fingertips have a rigid layer inside the fluid to grasp normal rigid objects. We experimentally showed the effectiveness of the gripper.