# Soft Gripper Design and Fabrication for Underwater Grasping
## 1 Introduction  
Current underwater technology permits accessing traditionally dangerous environments for divers using Atmospheric Diving Suits (ADSs), Remotely Operated Vehicles (ROVs), and Autonomous Underwater Vehicles (AUVs) [1, 2]. However, underwater manipulation using these systems has shown limited manipulation abilities in versatility and robustness terms, principally operating with soft or fragile objects and organisms. Using rigid claw-like end-effectors [3, 4] is quite common for performing easy and heavy mechanical works, such as wrist-rotation movements in construction or pipeline maintenance. Most advanced end-effectors use sophisticated force/torque sensors [5, 6, 7, 8] to close the control loop, minimizing damage and stabilizing the grasping operation. However, these end-effectors may not be suitable for complex underwater manipulation with different sources of uncertainty, such as currents in seawater, soft materials with large deformations, and delicate objects that require adapting to the geometry in the manipulation by distributing the grasping forces. Some examples of challenging underwater manipulation are underwater archeological recovery, biological sampling [1], and removal of dead fish in fish farms, to name but a few. Using soft materials rather than conventional metallic ones and strong polymers permits us to mimic the behavior of natural systems. The compliance of soft actuators adapts them to a diversity of shapes with simple control schemes, avoiding the need for modeling and controlling such soft nonlinear continuum actuators. This fact provides a key advantage over stiff systems in grasping and manipulating unknown objects. Since the early work of [PERSON] et al. [9, 10] designing a soft gripper composed of fingers with elastomeric chambers hydraulically actuated and permitting bending with multiple degrees of freedom, several soft devices for grasping and manipulation purposes have been developed. Soft robotics hands [11, 12] and grippers [13, 14, 15] allow us to manipulate delicate and complex objects by conforming to the object's shape and distributing the forces in the graspingoperation. This adaptation allows us to perform such tasks without precise positioning or using accurate geometric models of the object to grasp [16]. These soft devices must even interact with humans using materials with a module similar, in terms of rigidity, to that of soft biological materials [17]. Underactuated adaptive soft actuators and transmissions [18] and robotic hands [1] have shown to be effective in underwater grasping operations by load-sharing passively among combinations of soft actuators inspired by phalanges and fingers. However, manipulating complex objects and organisms often requires modifying or redesigning the soft actuator [19]. For this reason, we need suitable tools to accelerate the design and fabrication cycle. Additive manufacturing and Computer-Aided Design (CAD) tools allow us to accelerate such cycles. Another crucial aspect of underwater manipulation systems is the power source, which can restrict the feasibility and autonomy in certain conditions. Submarine manipulation systems using soft fluidic elastomer actuators [20] usually require a hydraulic system to operate in a wide depth working range [21,22]. In this work, we present the design and fabrication of a simple, low-cost, and easily deployable soft gripper for underwater manipulation, which can be deployed in a small underwater vehicle, with little buoyancy reserve. This implies that the additional weight that can be carried from bottom to surface is relatively small. The target application is the recollection of small objects or living organisms (coral, seaweed, mollusks, etc.). The proposal combines materials in the design and fabrication of the soft fluidic actuators composing the soft gripper. The underlying idea is to combine flexible thermoplastics with a softer material.