Towards Physical Underwater Robotic Assistance for Scuba Diver Movement in Confined Spaces

Summary

Scuba divers are taught to control their depth to avoid rapid ascents and descents, which could result in serious injuries such as gas embolisms and barotrauma.

Abstract Summary

Scuba divers are taught to control their depth to avoid rapid ascents and descents, which could result in serious injuries such as gas embolisms and barotrauma. However, many underwater tasks necessitate lateral control, maintaining distance between subsea structures such as coral reefs, submerged drilling instrumentation, or unexploded ordnance. In this work, we discuss a first-of-its-kind wearable robotic solution providing thruster-actuated directional guidance to a diver, as distinct from prior propulsive-assistance exoskeletons. We introduce ``Robotic Assisted Diver Movement in Confined Spaces'' (RADMCS), a wearable robot that assists divers in maintaining a fixed distance from subsea structures by leveraging perception techniques in monocular depth estimation and force-feedback from submersible thrusters to provide haptic feedback. Its small and compact form factor creates a foundational platform that could be expanded to include more sophisticated control and navigation behaviors. We present results from Institutional Review Board (IRB) in-water studies with eight human scuba diver participants on threshold sensitivity tests in both a closed-water swimming facility and ocean environments; distance-maintaining experiments in a closed-water facility; and form, fit, and function testing in the ocean. We demonstrate that relatively low thrust values (10 percent of maximum) allow robotic direction of a human's movement using the physical sensation of the robot's guidance.

Key Points

Scuba divers are taught to control their depth to avoid rapid ascents and descents, which could result in serious injuries such as gas embolisms and barotrauma.
However, many underwater tasks necessitate lateral control, maintaining distance between subsea structures such as coral reefs, submerged drilling instrumentation, or unexploded ordnance.
In this work, we discuss a first-of-its-kind wearable robotic solution providing thruster-actuated directional guidance to a diver, as distinct from prior propulsive-assistance exoskeletons.
We introduce ``Robotic Assisted Diver Movement in Confined Spaces'' (RADMCS), a wearable robot that assists divers in maintaining a fixed distance from subsea structures by leveraging perception techniques in monocular depth estimation and force-feedback from submersible thrusters to provide haptic feedback.
Its small and compact form factor creates a foundational platform that could be expanded to include more sophisticated control and navigation behaviors.

Literature Review

This work draws from both wearable guidance in haptics, which is the study of navigation using physical perturbation, and physical underwater human-robot interaction. Wearable Guidance and Assistive Technology . Global positioning systems promise precise localization in areas where signals are present.

System Design

Unlike exoskeletons that attach to the diver’s body directly, the proposed design of the RADMCS robot enables a less invasive integration with existing scuba diving technology. Namely, the RADMCS robot mounts onto the diver’s scuba tank using strapping mechanisms already employed by open-water scuba divers.

The design comprises two primary components: the external assembly, which has the mechanism for strapping to the diver; and the internal assembly, which houses the electronics subassembly and sensing technology. Fig.

System Design — Towards Physical Underwater Robotic Assistance for Scuba Diver Movement in Confined Spaces — Figure 3: Thruster configurations. The left image column shows the transverse thruster configuration that directs force perpendicular to the robot’s body, in the $\hat{x}$-direction. The right image column shows the longitudinal thruster configuration that directs force along the length of the robot’s body, in the $\hat{y}$-direction. The thrusters are labeled and referred to as shown in the figure for all future analysis.

Visual Control Methodology

We employ a linear control algorithm with saturation to limit our thruster outputs after a certain distance. Alg. 1 outlines the pseudocode for the control algorithm. The goal of the algorithm is to produce thruster PWM values in microseconds for $T1$ and $T2$. Let $I$ be an image of arbitrary dimensions.

Our control algorithm computes the distance $d^{i}$ between the camera and the target using the FindDistance function. A target can be any specific object or feature from which the algorithm can extract distance.

Visual Control Methodology — Towards Physical Underwater Robotic Assistance for Scuba Diver Movement in Confined Spaces — Figure 4: Still frames collected during the closed-water TS test for the $225$ mm transverse thruster configuration. During the “ascending” portion of the test, the thruster force-feedback increases in intensity, rotating the diver in the figure.

Human Study Evaluations

Under Institutional Review Board (IRB) approval, we conducted in-water human studies to evaluate the RADMCS system. Eight people with varying levels of scuba diving experience participated in a variety of in-water experiments to gauge TS and single-sided distance-maintaining wall following.

While the number of participants is lower compared to terrestrial haptics studies (see [ 7 ] which used $12$ participants), conducting underwater human studies creates a significant barrier to entry compared to its terrestrial counterpart.

Human Study Evaluations — Towards Physical Underwater Robotic Assistance for Scuba Diver Movement in Confined Spaces — (a) CW rotation/longitudinal thruster configuration.

Sources and Demonstrations

Figures are reproduced from Kutzke et al. See the full paper for experimental details and the project page, when the paper links one, for demonstrations and videos.