Autonomous Robotic Intervention using ROV
Master thesis
Date
2016Metadata
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- Institutt for marin teknikk [3436]
Abstract
This thesis proposes a semi-autonomous agent architecture for a Remotely Operated Vehicle(ROV). The purpose of this architecture is to apply control strategies from AutonomouslyOperated Vehicles (AUVs) onto ROVs, in order to perform certain subsea operations autonomously. As a result, an autonomous ROV (AROV) can be used to perform tasks thatare currently performed by human divers or by an operator through remote control. Thearchitecture increases the safety, reduces the costs, and minimizes the need for human intervention.
The agent architecture focuses on a general subsea operation, the approach and localizationof a Structure Of Interest (SOI) located on the seabed. For this purpose, a hybrid controlarchitecture is developed. The term hybrid describes the combination of deliberative andreactive control layers. The deliberative layer accounts for the slowly moving behaviorcomponents, taking the ROV from the surface to the SOI. It is comprised of six underlyingsystem states, dividing the mission into sub-problems. The states follow the mission anatomyin the order: (1) Launch, (2) Descent, (3) Transit, (4) Sonar tracking, (5) Camera trackingand (6) Inspection/Intervention. The reactive layer takes care of the contingency handling,i.e. the behavior of the vehicle when it is exposed to unexpected situations. The reactivebehavior implemented in this thesis is Obstacle/Collision Avoidance, using computer visiontechniques for detection of the obstacle. The reactive layer has priority in the controlexecution layer, which composes the third layer of the agent architecture, by decidingwhich behavior should be carried out.
The capability and limitations of the agent architecture are demonstrated through softwaresimulations and full-scale field experiments on the research vessel R/V Gunnerus using theROV Sub Fighter 30 k. Some behaviors are only simulated, such as feedback navigationusing sonar and camera data, and autonomous maneuvering of the manipulator s arm. Thisthesis aims to provide the architecture framework, and consequently, the optimization of thesub-behaviors has not been considered a priority of this work. Optimization of each stateshould be considered for future research on the subject. The result is an architecture steering the vehicle autonomously, according to the implemented deliberative and reactive behaviors. The agent architecture has the possibility of adding and removing an infinite amount of these behaviors, enabling for a variety of subsea operations. The results were quite satisfactory, both from simulations and field work. Deliberative and reactive behaviors were tested separately and simultaneously, using known SOIs and obstacles in the Trondheim fjord. All results confirmed the expected autonomous behavior of the vehicle, moving from the surface until the localization of the SOI and stationkeeping in front of it, using the sensors and equipment available.
This thesis shows that the agent architecture is a well-designed framework for increasingthe autonomy in ROV operations. Results imply that further research should be carriedout on the topic, such as optimization of each sub-behavior, implementation of stereo visionposition estimates and autonomous interventions/inspections. This thesis is considered apioneering contribution to autonomous ROV interventions, adding new results to previousresearch.