Design of an above water position determination system for a ship’s hull maintenance robot

Design of an above water position determination system for a ship’s hull maintenance robot

Feitsma, W.J.L.

Babuska, R. (mentor)
Borota, D. (mentor)
De Vet, C.P.M. (mentor)
Noordstrand, A.M. (mentor)

Mechanical, Maritime and Materials Engineering

Mechanical Engineering

Control Engineering

2016-04-22

Localization is vital for a ship’s hull maintenance robot such as the Fleet Cleaner robot. Not only is it key for automation of the robot, but it is also required to guarantee coverage and to produce inspection reports. Previous work on the position determination focussed on the under water localization and left the above water section as a partially open problem. For above water localization, standard techniques will not suffice due to the strict environmental and operational constraints and requirements. Hence the main goal of this thesis is: "design an above water position determination system for a ship’s hull maintenance robot". This goal is approached in three steps: conceptual design of the absolute above water setup, development of the proposed solution for the absolute above water localization, and development of the relative localization. In the conceptual design phase the optimal sensing principles are identified. Utilizing the constraints and requirements a solution is proposed: radio based time-of-flight measurements. The most decisive factors were the robustness to adverse weather and the low complexity. Sensors will be placed on beacons that will be used for underwater localization. A simultaneous localization and mapping algorithm is proposed to track the robot, allowing calibration of the beacons, which serve as position references, to be performed online. This is advantageous for meeting operational time constraints. For the proof of concept, further theoretical and experimental analysis is conducted. The main sources of error in range measurements are found: clock drift, dependency on received signal level, antenna performance and temperature offset. A two way timing policy, a correction based on the estimated power level, guidelines for antenna placement and a temperature based compensation are found to reduce these errors. Localization experiments using these methods on a 0-7 m range resulted in a maximum error of 0.3 m and on a 0-30 m range in a maximum error of 1 m. The experiments provide a proof of concept for tracking of the robot and online calibration of beacons. Relative sensors are applied to increase accuracy. The available systems are: a wheel encoder, an inertial measurement unit and the control signals. A mathematical model for movement on a flat surface, applicable to both wheel encoder and input model, is presented. Uncertainty in the vessel’s geometry makes formulation of a mathematical solution for the movement on curved surfaces a key problem for future development. The most important requirement for the future development is identified: the execution of experiments that resemble maintenance operation on full scale. Combining this with a mathematically formalized comparison of algorithms will lead to better estimation. The recommendations form a roadmap to the realization of a position determination system on operational scale.

http://resolver.tudelft.nl/uuid:c24cc6e3-b93e-4fee-9dc2-55bc77c2fa29

2021-03-22

Student theses

master thesis

(c) 2016 Feitsma, W.J.L.