G.N. Roberts

Designing a Fuzzy-like PD controller for an underwater robot

Abstract The design of a steering and depth control in terms of course-changing and course-keeping tracking mission and motion of an underwater vehicle is described in this paper. Fuzzy-like proportional derivative (PD) controller is used where the Fuzzy-like part of the controller is optimised based on its structure and parameter design aspects, whereas the scaling factors of the PD part is optimised based on the minimum number of experiments in a real environment. The experiments were planned using Taguchi design of experiments method. The experimental trials and their results are presented and analysed extensively.

Final experimental results of full scale fin/rudder roll stabilisation sea trials

Abstract The consequences of roll motions can seriously degrade the effectiveness of ship performance. In order to alleviate roll motions, ships are often equipped with fin stabilisers. Rudders can also generate roll motions and can be harnessed to function in congress with the fins to accrue enhanced levels of stabilisation. This paper reports on the final phase of full-scale sea trials utilising the existing rudders and fins on board a frigate-sized warship. where various control strategies were employed.

An Overview on Behaviour-Based Methods for AUV Control

Abstract Traditionally, deliberative reasoning methods based on a world model have been used to guide Autonomous Vehicles. Nevertheless, due to serious problems when dealing with complex and changing environments the alternative approach of reactive architectures appeared, directly coupling perception and action without any world representation. This paper describes the characteristics and variants of reactive architectures as well as four of the most suitable ones to guide Autonomous Underwater Vehicles: Schema-based approach, Subsumption, Process Description Language and Action Selection Dynamics. Each architecture is described and evaluated using an underwater simulator with an AUV model.

Extension of feasible region of control allocation for open-frame underwater vehicles

Abstract Standard pseudoinverse method for solution of the control allocation problem for overactuated open-frame underwater vehicles is able to find a feasible solution only on a subset of the attainable command set. This subset is called the feasible region for pseudoinverse. Some other methods, like direct control allocation or fixed-point iteration method, are able to find the feasible solution on the entire attainable command set. A novel, hybrid approach for control allocation, proposed in this paper, is based on integration of the pseudoinverse and the fixed-point iteration method. It is implemented as a two-step process. The pseudoinverse solution is found in the first step. Then the feasibility of the solution is examined analysing its individual components. If violation of actuator constraint(s) is detected, the fixed-point iteration method is activated in the second step. In this way, the hybrid approach is able to allocate the exact solution, optimal in the l 2 sense, inside the entire attainable command set. This solution minimises a control energy cost function, the most suitable criteria for underwater applications.

Fault Detection and Accommodation for ROVs

Abstract A new approach for fault detection and accommodation for remotely operated underwater vehicles is proposed in this paper. The proposed Fault Detection and Accommodation System (FDAS) consists of two subsystems: Fault Detection Subsystem (FDS) and Fault Accommodation Subsystem (FAS), The FDS uses fault detector units (FDU), associated with each thruster, to monitor their healthy state. Robust and reliable fault detection units are based on integration of self-organising maps and fuzzy logic clustering methods. These units are able to detect internal and external faulty states of a thruster. The FAS uses information provided by the FDS to accommodate faults and perform an appropriate reconfiguration, A control energy cost function is used as the optimisation criteria. In fault-free and faulty cases the FAS finds the optimal solution, which minimise this criteria. The proposed FDS is evaluated with data obtained during test trials.

Sea-trial experimental results of fin/rudder roll stabilisation

Abstract This paper reports on full-scale roll stabilisation trials on board a frigate-size Royal Naval warship. The trials entailed comparing the efficacy of the fins functioning alone, with the combined effects of the fins and rudders operating in congress to reduce roll motions. The rudders were employed in a supplementary role and no mechanical modifications were made. To afford a comparison of the results the data acquired is presented in the RMS form.

A fuzzy track-keeping autopilot for ship steering

In this paper a non-linear fuzzy autopilot for ship track-keeping is presented. The proposed autopilot has four inputs (actual and desired heading, rate of change of heading and offset from the desired path) and one output (command rudder angle). The track-keeping problem is decomposed into two subtasks: (i) follow the desired heading, and (ii) bring the ship onto the desired path and keep tracking. Internally, the autopilot consists of two autopilots that fulfil these tasks simultaneously. The proposed control scheme has been verified using a non-linear model of a Mariner-class vessel and steering mechanism under the influence of wave and current disturbances. Results presented show how such a control strategy enables improved tracking performance.

Thruster Fault Accommodation for Underwater Vehicles

Abstract This paper introduces a new approach associated with fault detection and accommodation for remotely operated underwater vehicles. The proposed fault detection and accommodation system (FDAS) consists of two subsystems: fault detection subsystem (FDS) and fault accommodation subsystem (FAS). The FDS uses fault detector units (FDU), associated with each thruster, to monitor their healthy state. Robust and reliable fault detection units are based on integration of self-organising maps and fuzzy logic clustering methods. The FAS uses information provided by the FDS to accommodate faults and perform an appropriate reconflguration. A control energy cost function is used as the optimisation criteria. In fault-free and faulty cases the FAS finds the optimal solution, which minimise this criteria. The feasible region concept, related with the problem of thruster velocity saturation, is described.

Reconfigurable control for ship steering

This paper is concerned with the application of a heuristic approach in the design of a fault-tolerant control system for ship steering. It proposes an advanced reconfigurable control system (RCS) for ship course changing/keeping and track keeping, robust to faults in actuator, gyrocompass and global positioning system (GPS) in the presence of disturbances (waves and currents). The proposed control scheme uses a reference model for compensation of signals from fault sensors and a compensator for reducing the loss of the control performance produced by a fault in the steering machine. In the case of the occurrence of the fault in one or more components, this control system minimizes loss in the control performance and gives enough time for operators to take appropriate action in order to reduce the risk of safety hazards and avoid severe consequences of the fault. The unavoidable penalty of degradation in control performance was found to be acceptable.

A Fuzzy Controller for Integrated Ship Motion Control

Abstract This paper describes The development of fuzzy controller for integrated control of the coupled yaw-roll motion of a container ship. The basic fuzzy rules used for designing an integrated multivariable rudder roll damping and yaw autopilot are discussed. A random search learning mechanism for automatically tuning the fuzzy controller parameters is presented. The efficiency and robustness of the controller are evaluated by a number of simulation tests conducted at different sea states. The results are used to evaluate the performance of the fuzzy controller in comparison with a conventional LQ design.