Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Proposal and Prototyping of Autopilot External Module for Underwater Robots
Tsukasa KITA, Toshinari TANAKA, Hiroyoshi SUZUKI
Infrastructure Digital Transformation Engineering Department,
Port and Airport Research Institute.
Yokosuka, Kanagawa, Japan

Naval Architecture and Ocean Engineering Depart., Osaka University.
Suita, Osaka, Japan

spaces at culverts are too small for UAVs to fly through. Furthermore,robots cannot receive radio waves from GNSS satellite at culverts. Hence,
they have to measure their own positions using a special method.
Therefore, special robots have been proposed for culvert inspection. Oneof the culverts in ports is the spaces of underneath piers. Inspection ofthat part has been perfomred by workers on boats. In places where boats
cannot enter, divers are used for this task. This task was performed in thepresence of waves and water currents, and a lot of effort was required toensure safety. Therefore, the use of robots in this scenario is required.
To solve this problem, Tanaka (2020) proposed a robot that can detect
its absolute position by measuring its relative position to piles using LRF
above the sea surface. Operators can control robot remotely while
grasping the position. In the future, it is expected that robots are used inthis regard instead of boats.
In contrast, most underwater inspections are still perfomred by divers inJapan, especially in ports, whose muddy seawater typically muddy. It isdifficult to grasp the surrounding situation. In addition, divers have towork near the structures. Divers could get caught on the protrusions andget injured. Moreover, with the recent increase in the size of ships, ports
are becoming deeper. Therefore, inspection and other tasks are becoming
more difficult. Therefore, the introduction of robots to inspect
underwater areas is requested.
However, underwater robots have not been widely introduced forunderwater inspection. One of the reasons for this is that operators musthave a high level of skill. Operators must control robots while notknowing their exact current position. It is difficult to confirm the positionof robots visually with eyes due to turbidity. In addition, images takenwith underwater cameras are not sufficiently clear to grasp thesurrounding structures without getting close. To solve this problem,automated robots that do not require operator training is required.
However, position detection is also the bottleneck in the automation ofunderwater robots that navigate near structures. It is difficult even withsensors. GNSS cannot work in the sea because radio waves areattenuated by seawater. Doppler velocity logger (DVL), which canestimate robot positions by integrating the velocity over time, cannot
always measure robot positions around structures because of reflections
from walls. Visual simultaneous localization and mapping (SLAM)
cannot be applied because turbidity prevents capturing clear images. It isABSTRACT
We proposed external modules for autopilot of underwater robots topromote the use of robots in port inspection. This research focuses oncommercially available small underwater robots. We examined therequirements for the external module and the procedure of the target task.
Then, a prototype module was developed. The module was constructed
for brief visual checks for the wall of sheet pile quays. Afterward, themodule was mounted on a robot and demonstrated its ability toautomatically navigate along a wall while taking images in a tank test.

KEY WORDS: Underwater robot, Inspection robot, Navigation
INTRODUCTION
In Japan, inspection of infrastructure is being actively performed.
Infrastructures were rapidly developed in the 1960s. Infrastructures thatare more than 50 years old are still in use. In the 2010s, an accident
involving slabs falling from the ceiling of a highway tunnel highligted
the issue of aging infrastructures. As a result, maintenance, management,and inspection of aging infrastructures began to be actively discussed.
Discussions of inspection of marine infrastructures such as port
structures also started.
Automatic inspection of land-based infrastructures using robots andremote inspection have been advanced. One of the basic inspection
methods for infrastructure is to visually check for cracks and otherdeformation. In the past, these tasks were performed by humans whenfacilities were out of service or restricted. Subsequently, to reduce thetime of suspension or restriction, inspection have been performed using
various devices. For instance, unmanned aerial vehicles (UAVs)
equipped with cameras are used to inspect bridges. These devices havecontributed to shortening the inspection time and lowering the cost. The
use of robots for port inspection has been discussed; the discussion hasbeen advanced, especially in surveying shapes of top surfaces ofstructures. Many researches in recent years have focused on the use ofUAVs. For instance, Henriques et al. (2017) surveyed the shape of rubble
mound breakwaters using UAVs.
In addition, the use of robots at culverts is being discussed. Some of1161