Citation: Wang, B.; Chen, Y.; Wu, Y.;
Lin, Y.; Peng, S.; Liu, X.; Wu, S.; Liu,
S.; Yi, J.; Polygerinos, P.; et al. An
Underwater Glider with
Muscle—Actuated Buoyancy Control
and Caudal Fin Turning. Machines
2022, 10, 381. https://doi.org/
10.3390/machines10050381
Academic Editors: Jacopo Aguzzi,
Giacomo Picardi,
Damianos Chatzievangelou,
Simone Marini, Sascha Flögel,
Sergio Stefanni, Peter Weiss and
Daniel Mihai Toma
Received: 4 April 2022
Accepted: 4 May 2022
Published: 16 May 2022
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2022 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
Article
An Underwater Glider with Muscle—Actuated Buoyancy
Control and Caudal Fin Turning
Biao Wang
1,2,3,†
, Yishan Chen
1,2,3,†
, Yige Wu
1,2,3
, Yi Lin
1,2,3
, Sijie Peng
1,2,3
, Xiaohan Liu
1,2,3
, Shijian Wu
1,2,3
,
Sicong Liu
1,2,3
, Juan Yi
1,2,3
, Panagiotis Polygerinos
4
and Zheng Wang
1,2,3,5,
*
1
Shenzhen Key Laboratory of Biomimetic Robotics and Intelligent Systems, Department of Mechanical and
Energy Engineering, Southern University of Science and Technology, Shenzhen 518000, China;
11811116@mail.sustech.edu.cn (B.W.); 11930357@mail.sustech.edu.cn (Y.C.);
11811138@mail.sustech.edu.cn (Y.W.); 11911931@mail.sustech.edu.cn (Y.L.);
11910702@mail.sustech.edu.cn (S.P.); 11911925@mail.sustech.edu.cn (X.L.);
12132305@mail.sustech.edu.cn (S.W.); liusc@sustech.edu.cn (S.L.); yij3@sustech.edu.cn (J.Y.)
2
Guangdong Provincial Key Laboratory of Human Augmentation and Rehabilitation Robotics in Universities,
Southern University of Science and Technology, Shenzhen 518000, China
3
Department of Mechanical and Energy Engineering, Southern University of Science and Technology,
Shenzhen 518000, China
4
Control Systems and Robotics Laboratory (CSRL), Department of Mechanical Engineering,
Hellenic Mediterranean University, 71410 Crete, Greece; polygerinos@hmu.gr
5
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
* Correspondence: wangz@sustech.edu.cn; Tel.: +86-75588015370
† These authors contributed equally to this work.
Abstract:
Underwater robotic gliders exploit gravity and buoyancy for long-distance cruising with
ultra-low energy consumptions, making them ideal for open ocean surveying operations. However,
the gliding-based motion generation principle also prevents their maneuverability, limiting their use
in the short distances that are usually encountered in harbors or coastal scenarios. In this work, an
innovative underwater glider robot is developed, enabling maneuverability through the introduction
of an efficiently actuated caudal fin with bidirectional turning capabilities. In addition, modular
actuator units, based on soft actuated materials, are integrated to control pitch angle by dynamically
shifting the center of mass from the center of buoyancy. As a result, the high energy efficiency
feature of the gliders is maintained, while high maneuverability is also achieved. The design concept,
modeling of key components, and framework for control are presented, with the prototyped glider
tested in a series of bench and field trials for validation of its motion performance.
Keywords: underwater glider; soft muscle actuation; modularized design
1. Introduction
Measuring water temperature, salinity, conductivity, the direction of sea currents, and
mapping of the seafloor are just a few of the many operations performed today using
unmanned underwater vehicles (UUVs) [
1
,
2
]. Such submersible robots can be operated
remotely or autonomously. They are usually employed to assist with a range of activities,
ranging from oceanographic studies in deep-sea explorations to oceanic warfare [
3
,
4
]. Re-
cent review studies summarize the advancements in autonomous underwater vehicles
(AUVs) [
4
–
6
]. These studies highlighted the usefulness of such robotic systems and numer-
ous differences in their operating principles. While earlier designs were mostly bulky, with
the advances in functional materials, sensors, and batteries, AUVs transitioned to become
more efficient and accessible [
7
,
8
]. Historically, AUVs with wings that glide by utilizing
water buoyancy were first reported with far superior efficiency over surface floating ve-
hicles or propeller-based underwater vehicles [
9
]. Since then, a number of gliders were
designed and tested [10–13].
Machines 2022, 10, 381. https://doi.org/10.3390/machines10050381 https://www.mdpi.com/journal/machines
