Citation: Jiang, D.; Zheng, T.; Yang,
G.; Tian, Y.; Fang, Z.; Li, H.; Zhang,
C.; Ye, H. Design and Analysis of a
Stiffness-Enhanced 3-PPS Parallel
Mechanism for Fault-Tolerant
Underwater Vectored Thrusters.
Machines 2022, 10, 88. https://
doi.org/10.3390/machines10020088
Academic Editors: Giovanni
Boschetti and João Miguel da
Costa Sousa
Received: 6 January 2022
Accepted: 19 January 2022
Published: 25 January 2022
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Article
Design and Analysis of a Stiffness-Enhanced 3-PPS Parallel
Mechanism for Fault-Tolerant Underwater Vectored Thrusters
Dexin Jiang
1,2,3
, Tianjiang Zheng
2,3,
* , Guilin Yang
2,3
, Yingzhong Tian
1
, Zaojun Fang
2,3
, Huamin Li
2,3
,
Chi Zhang
2,3
and Hongwu Ye
2,4
1
School of Mechatronic Engineering and Automation, Shanghai University, Shanghai 200444, China;
jiangdexin@nimte.ac.cn (D.J.); troytian@shu.edu.cn (Y.T.)
2
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences,
Ningbo 315201, China; glyang@nimte.ac.cn (G.Y.); fangzaojun@nimte.ac.cn (Z.F.); hmli@nimte.ac.cn (H.L.);
zhangchi@nimte.ac.cn (C.Z.); yehowu@126.com (H.Y.)
3
Zhejiang Key Laboratory of Robotics and Intelligent Manufacturing Equipment Technology,
Chinese Academy of Sciences, Ningbo 315201, China
4
Mechanical & Electrical Engineering School, Zhejiang Fashion Institute of Technology, Ningbo 315201, China
* Correspondence: zhengtianjiang@nimte.ac.cn
Abstract:
Vectored thrusters can significantly improve the maneuverability of underwater vehicles.
However, due to the harsh underwater environment and severe working conditions, the thrust-
vectoring device needs to be designed with high stiffness and high reliability. In this paper, a
3-degree-of-freedom (3-DOF) 3-P
P
S parallel mechanism is employed for the 2-DOF thrust-vectoring
device, which has the advantages of high stiffness and a certain level of fault tolerance. The stiffness
of the 3-P
P
S parallel mechanism is enhanced through employing additional passive prismatic joints.
Based on the zero-torsion characteristics of the parallel mechanism, closed-form solutions are obtained
for displacement analyses, and the orientation workspace of the moving platform under an actuation
failure, i.e., one of the active prismatic joints is locked, is particularly investigated through an equi-
volumetric partition method. To analyze the orientation workspace distribution under the actuation
failure, the fault-tolerant workspace and the maximum inscribed workspace are defined. Furthermore,
a new fault-tolerant index is proposed to evaluate the fault tolerance of the parallel mechanism. The
proposed design analysis is validated through experiments on an engineering prototype of the
parallel mechanism.
Keywords:
underwater vectored thrusters; design analysis; 3-P
P
S parallel mechanism; stiffness
enhancement; fault-tolerant workspace
1. Introduction
Underwater vehicles have been extensively employed in ocean engineering, such as
oceanographic exploration [
1
,
2
], offshore gas extraction [
3
], and deep water mining [
4
]. Ow-
ing to the harsh underwater environments and severe working conditions, the underwater
vehicle needs to be designed with high maneuverability and high reliability. Therefore, the
design of the vector propulsion system becomes crucial for the underwater vehicle.
To improve the motion performance of underwater vehicles, there are mainly two
approaches, i.e., a vector water-jet propulsion system [
5
,
6
] and vector propulsion system
based on a propeller [
7
,
8
], to realize vector propulsion. However, the complex mechanical
structure of the vector water jet propulsion reduces the system’s reliability [9]. In compar-
ison, the vector propulsion system based on the propeller not only has the priorities of
flexible assemble mode and high propulsion efficiency, but also maintains high maneuver-
ability and a certain reliability [
10
,
11
]. Thus, the vector propulsion system based on the
propeller is a more suitable option to improve the motion performance of the underwater
vehicles in common applications.
Machines 2022, 10, 88. https://doi.org/10.3390/machines10020088 https://www.mdpi.com/journal/machines
