Gong Z et al. (2019), An Opposite-Bending-and-Extension Soft Robotic ...

ECB-ART-49925

Front Robot AI 2019 Apr 24;6:26. doi: 10.3389/frobt.2019.00026.

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An Opposite-Bending-and-Extension Soft Robotic Manipulator for Delicate Grasping in Shallow Water.

Gong Z , Chen B , Liu J , Fang X , Liu Z , Wang T , Wen L .

Abstract
Collecting seafood animals (such as sea cucumbers, sea echini, scallops, etc.) cultivated in shallow water (water depth: ~30 m) is a profitable and an emerging field that requires robotics for replacing human divers. Soft robotics have several promising features (e.g., safe contact with the objects, lightweight, etc.) for performing such a task. In this paper, we implement a soft manipulator with an opposite-bending-and-extension structure. A simple and rapid inverse kinematics method is proposed to control the spatial location and trajectory of the underwater soft manipulator's end effector. We introduce the actuation hardware of the prototype, and then characterize the trajectory and workspace. We find that the prototype can well track fundamental trajectories such as a line and an arc. Finally, we construct a small underwater robot and demonstrate that the underwater soft manipulator successfully collects multiple irregular shaped seafood animals of different sizes and stiffness at the bottom of the natural oceanic environment (water depth: ~10 m).

PubMed ID: 33501042
PMC ID: PMC7805983
Article link: Front Robot AI

Article Images: [+] show captions

	Figure 1. (a) Seafood collection by a human diver. (b) The snapshot of the underwater robot with a soft manipulator for grasping fragile sea animals. Multiple cameras are applied to provide underwater vision. The length of scale bar is 100 mm.
	Figure 2. The design and principle mechanics of the underwater soft manipulator. (a) An overall side image of the underwater soft manipulator (scale bar 50 mm). (b) The underwater soft manipulator is applied modularized design that consisted of two bending segments, an elongating segment, and a soft gripper. θ1 and θ2 represent the bending angles of the two bending segments, and α represents the horizontal angle of the manipulator tip. The manipulator is actuated with an opposing curvature where θ1 = θ2 and α = 0. (c) The two bending segments had a joining angle of 180°. (d) θ1, θ2, and α are verified in one actuation with opposing curvature. The two bending angles (θ1, θ2) are almost equal, and the horizontal angle (α) is zero at each moment. (e) The fiber-reinforced elongating segment. The yellow arrow indicates the direction of elongation.
	Figure 3. Kinematics of the underwater soft manipulator. (a) The two bending segments of the underwater soft manipulator are always actuated with opposing curvatures. Thus, the bending angles are always equal (θ1 = θ2). (b) The kinematic transformation map. We focused on inverse kinematics (f inv) from the position parameters (xi, yi, zi) to chamber lengths (li1, li2, li3, le) via arc parameters (κi, φi, θi). (c) Geometric schematic in a bending segment, where φi represents the rotation angle around the z-axis; θi represents the bending angle around the y-axis; ri represents the radii of the bending curve; and Li represents the centerline length of the bending segment. (d) Geometric schematic of the cross-section, where h represents the distance between the arm surface and the center of the cross-section.
	Figure 4. The multi-channel pneumatic actuation system for the underwater soft manipulator. The system contains a microcontroller, power source, DA converter, ten proportional valves, and ten air pressure sensors.
	Figure 5. Chamber lengths of the bending segments (red) and elongating segment (black) as a function of the actuation pressure.
	Figure 6. Control location error as a function of operating radius d (0 to 100 mm).
	Figure 7. (a) The simulation of operating workspace of the underwater soft manipulator. (b) The front view of the workspace. (c) The top view of the workspace.
	Figure 8. Controlled soft manipulator following trajectories of a line (A) and an arc (C). Distance response with time while tracking (B) the line trajectory and (D) the arc trajectory.
	Figure 9. System architecture of the underwater grasping robot. The system contains human-machine Interface, driving system and the underwater robot system. The underwater robot is operated to approach the target seafood animals by the human operator. Then the underwater soft manipulator is controlled pick and place the sea animals via inverse kinematics model. The whole process is monitored by cameras which facilitates the remote control of human operator.
	Figure 10. Undersea grasping with the underwater soft manipulator mounted on a small underwater robot. (a) The underwater grasping is demonstrated in the natural undersea environment at 10 m depth. (b,c) Grasping undersea animals (echini and sea cucumbers) with soft manipulator.

References [+] :

Calisti, An octopus-bioinspired solution to movement and manipulation for soft robots. 2011, Pubmed