A Partially Filled Jamming Gripper for Underwater Recovery of Objects Resting on Soft Surfaces

In this paper we demonstrate a universal jamming gripper with a partially filled membrane that can pick up submerged objects resting on soft substrates. Jamming grippers take advantage of the phenomenon of particle jamming to control the compliance of an end effector membrane. Changes in internal membrane pressure are used to transition the membrane between hard and soft states. The effort was motivated by the need for tools to sample artifacts on deep sea shipwrecks, which are often found resting on waterlogged timbers, or partially buried in fine, loose sediment. Limiting downward force protects the target, and reduces the likelihood that it will be pushed down in to the substrate, which could lead to a failed grasp. In benchtop tests, the downward force, and the ratio of maximum lifting force to downward force, are shown to be strongly dependent on the initial volume of particles and fluid in the gripper membrane. The gripper achieves lifting forces 6.7 times the downward force on targets with high aspect ratios. Experiments in a fresh water tank demonstrate the ability to grasp objects resting on soft sediment, and compliant foam. Finally, experiments at sea demonstrate that the end effector functions at depths of more than 1000m seawater, successfully grasping a range of irregular objects.