A Dexterous, Glove-Based Teleoperable Low-Power Soft Robotic Arm for Delicate Deep-Sea Biological Exploration

Abstract

Modern marine biologists seeking to study or interact with deep-sea organisms are confronted with few options beyond industrial robotic arms, claws, and suction samplers. This limits biological interactions to a subset of "rugged" and mostly immotile fauna. As the deep sea is one of the most biologically diverse and least studied ecosystems on the planet, there is much room for innovation in facilitating delicate interactions with a multitude of organisms. The biodiversity and physiology of shallow marine systems, such as coral reefs, are common study targets due to the easier nature of access; SCUBA diving allows for in situ delicate human interactions. Beyond the range of technical SCUBA (~150 m), the ability to achieve the same level of human dexterity using robotic systems becomes critically important. The deep ocean is navigated primarily by manned submersibles or remotely operated vehicles, which currently offer few options for delicate manipulation. Here we present results in developing a soft robotic manipulator for deep-sea biological sampling. This low-power glove-controlled soft robot was designed with the future marine biologist in mind, where science can be conducted at a comparable or better means than via a human diver and at depths well beyond the limits of SCUBA. The technology relies on compliant materials that are matched with the soft and fragile nature of marine organisms, and uses seawater as the working fluid. Actuators are driven by a custom proportional-control hydraulic engine that requires less than 50 W of electrical power, making it suitable for battery-powered operation. A wearable glove master allows for intuitive control of the arm. The manipulator system has been successfully operated in depths exceeding 2300 m (3500 psi) and has been field-tested onboard a manned submersible and unmanned remotely operated vehicles. The design, development, testing, and field trials of the soft manipulator is placed in context with existing systems and we offer suggestions for future work based on these findings.

Figure 1

Overview of the deep-sea soft robotic arm system. (A) Control of actuators is achieved using a sensorized wireless glove, which coordinates the control of independent proportional valves that distribute pressure to the arm and end-effector actuators. (B) A custom open-circuit seawater engine regulates hydraulic pressure to independent ports, and can operate at depths of at least 2500 m. (C) The soft arm, consisting of bending, rotary, and gripping modules, can be mounted independently or as part of an existing manipulator system.

Figure 2

Examples of prior work on versatile soft grippers for deep-sea biological sampling. (A) “Boa” style fiber-reinforced actuator grasping a whip coral, and (B) four finger bellows-style actuator grasping a brittle scleractinian coral at 100 m in the Gulf of Eilat, Israel. (C) A two finger bellows actuator grasping a glass sponge at 300 m depth at Carandolet Reef, Phoenix Islands. Green laser dots at left side of image are 10 cm apart. (D) Three finger gripper with bellows-type actuators, grasping a holothurian at 1800 m in the Channel Islands National Marine Sanctuary, California.

Figure 3

(A) Workspace of a five-module soft arm, mechanically grounded at the uppermost vertical position. Rotary modules in the arm are shown in blue, bending in red, and a three-finger gripping module is mounted at the distal end. (B) The same workspace, viewed at a different perspective.

Figure 4

Hydraulic schematic and image of the open-circuit seawater hydraulic engine. The electronics housing contains both pump and valve control components.

Figure 5

Logarithmic power comparison of several leading deep-sea manipulator systems. All are actuated hydraulically with the exception of ECAGroups’ 5 E Mini (www.ecagroup.com), which uses electronic linear and rotary actuators. The HydroLek MiniGauntlet (www.hydro-lek.com) is considered the industry standard small form-factor hydraulic manipulator, typically used on lightweight ROV’s that are limited in the power and payload they can provide for manipulation.

Figure 6

(A) Images of wireless glove controller; the reader is referred to Vogt & Wood for a detailed description of this system. (B) Subsea valve controller board, which receives serial commands from the glove controller’s topside software. The board is based on dual 32-bit ARM microcontrollers, which send 0–24VDC output signals directly to each proportional valve.

Figure 7

Field testing in the Fernando de Noronha Archipelago, Brazil using a Triton 3K3 manned submersible. (A) Image sequence of the soft manipulator grasping a midwater pyrosome (Pyrosoma atlanticum) in the water column, as observed from a diver. (B) The soft manipulator articulating upwards to grasp a coral at approximately 300 m depth and (C) downwards to grasp a sponge. (D) Manipulator straightened out to approach the deep-sea octopus Cirroteuthidae murrayi at approximately 700 m. Images are taken from frames of a Red Digital 8 K Dragon pan-tilt camera mounted to the outside of the submersible.