A Soft Robotic Gripper With Neutrally Buoyant Jamming Pads for Gentle Yet Secure Grasping of Underwater Objects

Delicate grasping of complex diverse objects is a challenging task for underwater vehicles, such as remotely operated vehicles (ROVs). In this article, a novel controllably compliant soft robotic underwater gripper is presented, which uses two neutrally buoyant particle jamming pads to safely and securely grasp arbitrarily shaped objects, including fragile and/or massive targets. Antagonistic low-friction rolling diaphragm hydraulic cylinders are used to control the compliance of the jaw closure to passively limit the total force applied during the approach. The antagonistic hydraulic cylinders also compensate for the volume reduction of the pads during the jamming process while still enabling rigid grasp during manipulation. Soft finger-like fiber-reinforced actuators are used to maintain the shape of pads without introducing rigid elements. Force limitation is demonstrated by the ability to pick up fragile objects without breakage and to surround soft targets without excessive deformation of the object. We present the overall design, experimental setup, and in-water testing using a compact ROV-based hydraulic drive system. The resulting system has demonstrated capability for grasping a diverse range of objects that vary widely in terms of weight, size, and geometry, largely enabled by the hybrid design of soft grippers guiding jamming pads into optimal configurations.