  Robot grasping is subject to an inherent tradeoff: Grippers with a large span
typically take a longer time to close, and fast grippers usually cover a small
span. However, many practical applications of soft grippers require the ability
to close a large distance rapidly. For example, grasping cloth typically
requires pressing a wide span of fabric into a graspable cusp. Here, we
demonstrate a human-finger-inspired snapping gripper that exploits elastic
instability to achieve reversible rapid closure over a wide span. Using
prestressed semi-rigid material as the skeleton, the gripper fingers can widely
open (86 ~) and rapidly close (46 ms) following a trajectory similar to that of
a thumb-index finger pinching which is 2.7 times and 10.9 times better than the
reference gripper in terms of span and speed, respectively. We theoretically
give the design principle, simulatively verify the method, and experimentally
test this gripper on a variety of rigid, flexible, and limp objects and achieve
good adaptivity and mechanical performance. This research helps bridge the gap
between strong industry manipulators and safe human-interactive robotic hands.
