Octopus-Inspired Underwater Soft Robotic Gripper with Crawling and Swimming Capabilities

Abstract

Can a robotic gripper only operate when attached to a robotic arm? The application space of the traditional gripper is limited by the robotic arm. Giving robot grippers the ability to move will expand their range of applications. Inspired by rich behavioral repertoire observed in octopus, we implement an integrated multifunctional soft robotic gripper with 6 independently controlled Arms. It can execute 8 different gripping actions for different objects, such as irregular rigid/soft objects, elongated objects with arbitrary orientation, and plane/curved objects with larger sizes than the grippers. Moreover, the soft gripper can realize omnidirectional crawling and swimming by itself. The soft gripper can perform highly integrated tasks of releasing, crawling, swimming, grasping, and retrieving objects in a confined underwater environment. Experimental results demonstrate that the integrated capabilities of multimodal adaptive grasping and omnidirectional motions enable dexterous manipulations that traditional robotic arms cannot achieve. The soft gripper may apply to highly integrated and labor-intensive tasks in unstructured underwater environments, including ocean litter collecting, capture fishery, and archeological exploration.

Fig. 1.

A depiction of the mission profile and design of the octopus-inspired underwater soft gripper system. The gripper integrates adaptive grasping, omnidirectional crawling, and 3D swimming capabilities.

Fig. 2.

Soft Arm design and the principle of actuation. (A) Illustration of the soft Arm. The soft gripper consists of 6 Arms with 5 suckers on each Arm. (B) Simulation of the finite-element model (left) and experimental result of a soft Arm (right) under an applied pressure of 120 kPa. (C) Bending angle of the Arm under air and water actuation. (D) The load capacity test corresponds to each sucker point on the Arm driven by 2 fluids (water or air). Error bars show standard deviation from 4 tests. (E) Schematic showing the test procedure for underwater adhesive switch characteristics and simulation of the sucker. (F) Changes in the pre-adhesion and negative-pressure force of suckers of different diameters peeled off in the vertical direction. Error bars show standard deviation from 4 tests. (G) Suction during vertical peeling of an Arm adhered to a flat substrate from different positions. Error bars show standard deviation from 4 tests.

Fig. 3.

Performance characterization of the soft gripper. (A) The 2-dimensional (2D) layered design of the soft gripper (the design details of the clamp can be found in Fig. S8). (B) Three actuation principles of the soft gripper and the corresponding simulation and experimental results. (C to E) Vertical load capacity test for actuation principles II (C), IV (D), and VI (E) with a soft gripper gripping a 90-mm-diameter cylinder at 140-kPa pressure. During these tests, the soft gripper was fixed to the testbed, and the horizontal cylinder was positioned at the center of the gripper. Then, the soft Arms were actuated to the predefined pressures. The linear stage pulls the cylinder at a fixed velocity (12.5 mm s⁻¹ ) until the cylinder separates from the soft gripper. (F) The suction is generated by the soft gripper in the suction mode when the vertical peeling position is at the center and the edge, respectively. Error bars show standard deviation from 4 tests.

Fig. 4.

Dexterous manipulation of the soft gripper in underwater scenarios. (A) Illustration of the soft gripper grasping and collecting objects. Soft grippers approach objects–grasp–lift–release them into a storage bag. (B) Several common types of underwater litter collection. (C) Grab a light bulb, fishing net, brush pot, cube, soda can, plastic bottle, mobile phone, and plastic bag, respectively, and put them into the storage bag. (D) Seafood fishing. (E) Grab sea snail, tortoise, scallop, and sea cucumber and put them into the storage bag. (F) The soft gripper is driven by actuation principle VI and the suction mode to gently pick up and put down the vase underwater. (G) Handle the porcelain (plate, bowl, and jar) gently underwater. Scale bar, 10 mm.

Fig. 5.

Movement performance of the gripper. (A) Step lengths corresponding to gaits produced by actuating different numbers of Arms. The motion schematics for each gait can be found in Fig. S14. Error bars show standard deviation from 4 tests. (B) Illustration of the fastest gait. This gait is achieved by actuating any 2 Arms separated by an unactuated Arm in between and moving in a given direction. (C) Top and side views of gait 2-2 in progress. The maximum speed at which the gripper crawls is 25 mm/s. (D to F) The path that the gripper performs agile omnidirectional crawling underwater. It can realize the crawling of □ (D), △ (E), and 8 (F) paths, respectively. (G) Vertical swimming is achieved by actuating the 6 Arms of the soft gripper simultaneously. (H) Inclined swimming is achieved by actuating different Arms during vertical swimming to apply perturbations, turning off the pump, and falling in a desired direction. Swimming in 3D enables swimming to the top and across objects while crawling. Scale bar, 10 mm.

Fig. 6.

Grasping in confined space. (A and B) Confined space with only one entrance and an object inside that cannot be touched by the robotic arm. (C) Illustration of soft gripper moving and grasping. The circular dashed line represents the position of the soft gripper. First, release the soft gripper and grasp the handle to open the entrance. The soft gripper then goes through the hole and reaches the inside of the tank. Next, across the obstacle inside the tank to reach the object. Finally, adjust the position of the soft gripper to complete the grasping and recycling of the object. Scale bar, 40 mm. The yellow words represent different Arms and the waveforms of the control signal.