Abstract
The overall control system for an open-frame Remotely Operated Vehicle (ROV) is typically built from three subsystems: guidance, navigation and control (GNC). The control allocation plays a vital role in the control subsystem. Typically, open-frame underwater vehicles have p actuators (thrusters) for the motion in the horizontal plane, and the control allocation problem, in this case, is very complex and hard to visualise, because the normalised constrained control subset is a p-dimensional unit cube. The aim of this paper is to give a clear picture and a geometric interpretation of the problem and to introduce a hybrid method, based on the integration of a weighted pseudoinverse and the fixed-point method. The main idea of the hybrid method is visualised, and the deep geometric insight is provided using a “virtual” ROV in low-dimensional control spaces, including visualisation of the attainable command set, solution lines, control energy spheres and the role of pseudoinverse and fixed-point iterations. The same concepts are then extended to higher-dimensional cases, for open-frame ROV with four X-shaped (vectored) horizontal thrusters, which is one of the most common thruster configurations for commercial ROVs. The proposed hybrid method has been developed, integrated into a generic fault-tolerant ROV control system and evaluated in virtual and real-world environments off the west coast of Ireland using observation-class ROV Latis and work-class ROV Étaín.
Highlights
A fault is the primary cause of changes in the system structure or parameters that eventually leads to degraded system performance or even the loss of the system function
This paper introduces a geometric insight into the control allocation problem for over actuated open-frame underwater vehicles
The same concepts are extended to higher-dimensional cases, for open-frame Remotely Operated Vehicle (ROV) with four X-shaped horizontal thrusters
Summary
A fault is the primary cause of changes in the system structure or parameters that eventually leads to degraded system performance or even the loss of the system function. Disturbances and model uncertainties are nuisances which are known to exist, but whose effects on the system performance are handled by appropriate measures like filtering or robust design. On another side, the FTC system is designed to detect the faults and remove their effects by remedial actions, i.e., it is aimed to change the control law in order to cancel the effects of the faults or to attenuate them to an acceptable level. Subject to Bu = v is given by where the matrix B†Wu u = B†Wu v (18) −1 † T −1 T −1 B†Wu = W−1.
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