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-PPS 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-PPS 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.
Highlights
Underwater vehicles have been extensively employed in ocean engineering, such as oceanographic exploration [1,2], offshore gas extraction [3], and deep water mining [4]
This paper focuses on the stiffness-enhancement design and fault tolerance measurement issues of a 3-DOF parallel mechanism for the 2-DOF thrust-vectoring device in an underwater thruster
Compared with the traditional 3-PPS parallel mechanism, a center base with redundant passive prismatic joints is added in the new design, which significantly shorten the distance Lt between the moving platform and the base without changing the kinematic characteristics
Summary
Underwater vehicles have been extensively employed in ocean engineering, such as oceanographic exploration [1,2], offshore gas extraction [3], and deep water mining [4]. For the underwater vehicle, the underwater vectored thruster based on a parallel mechanism is able to achieve high reliability, and obtain high maneuverability through regulating the thrust direction. The 6DOF Stewart-Gough platform used as a thrust-vectoring device has been applied in an underwater robot called REMO I, but the additional 4-DOF reduces its manufacturing economy and increases its system complexity [25]. To address these problems, the 3DOF parallel mechanism is a priority candidate. This paper focuses on the stiffness-enhancement design and fault tolerance measurement issues of a 3-DOF parallel mechanism for the 2-DOF thrust-vectoring device in an underwater thruster.
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