Autonomous ROV inspections of aquaculture net pens using DVL

This article presents a method for guiding a remotely operated vehicle (ROV) to autonomously traverse an aquaculture net pen. The method is based on measurements from a Doppler velocity log (DVL) and uses the measured length of the DVL beam vectors to approximate the geometry of a local region of the net pen in front of the ROV. The ROV position and orientation relative to this net pen approximation are used as inputs to a nonlinear guidance law. The guidance law is based upon the line-of-sight (LOS) guidance law. By utilizing that an ROV is fully actuated in the horizontal plane, the crosstrack error is minimized independently of the ROV heading. A Lyapunov analysis of the closed-loop system with this guidance law shows that the ROV is able to follow a continuous path in the presence of a constant irrotational ocean current. Finally, results from simulations and experiments demonstrating the performance of the net pen approximation and control system are presented.acceptedVersio

State relativity and speed-allocated line-of-sight course control for path-following of underwater vehicles

Path-following is a primary task for most marine, air or space crafts, especially during autonomous operations. Research on autonomous underwater vehicles (AUV) has received large interests in the last few decades with research incentives emerging from the safe, cost-effective and practical solutions provided by their applications such as search and rescue, inspection and monitoring of pipe-lines ans sub-sea structures. This thesis presents a novel guidance system based on the popular line-of-sight (LOS) guidance law for path-following (PF) of underwater vehicles (UVs) subject to environmental disturbances. Mathematical modeling and dynamics of (UVs) is presented first. This is followed by a comprehensive literature review on guidance-based path-following control of marine vehicles, which includes revised definitions of the track-errors and more detailed illustrations of the general PF problem. A number of advances on relative equations of motion are made, which include an improved understanding of the fluid FLOW frame and expression of its motion states, an analytic method of modeling the signs of forces and moments and the proofs of passivity and boundedness of relative UV systems in 3-D. The revision in the relative equations of motion include the concept of state relativity, which is an improved understanding of relativity of motion states expressed in reference frames and is also useful in incorporating environmental disturbances. In addition, the concept of drift rate is introduced along with a revision on the angles of motion in 3-D. A switching mechanism was developed to overcome a drawback of a LOS guidance law, and the linear and nonlinear stability results of the LOS guidance laws have been provided, where distinctions are made between straight and curved PF cases. The guidance system employs the unique formulation and solution of the speed allocation problem of allocating a desired speed vector into x and y components, and the course control that employs the slip angle for desired heading for disturbance rejection. The guidance system and particularly the general course control problem has been extended to 3-D with the new definition of vertical-slip angle. The overall guidance system employing the revised relative system model, course control and speed allocation has performed well during path-following under strong ocean current and/or wave disturbances and measurement noises in both 2-D and 3-D scenarios. In 2-D and 3-D 4 degrees-of-freedom models (DOF), the common sway-underactuated and fully actuated cases are considered, and in 3-D 5-DOF model, sway and heave underactuated and fully actuated cases are considered. Stability results of the LOS guidance laws include the semi-global exponential stability (SGES) of the switching LOS guidance and enclosure-based LOS guidance for straight and curved paths, and SGES of the loolahead-based LOS guidance laws for curved paths. Feedback sliding mode and PID controllers are applied during PF providing a comparison between them, and simulations are carried out in MatLab

Path following of an underactuated AUV based on fuzzy backstepping sliding mode control

This paper addresses the path following problem of an underactuated autonomous underwater vehicle (AUV) with the aim of dealing with parameter uncertainties and current disturbances. An adaptive robust control system was proposed by employing fuzzy logic, backstepping and sliding mode control theory. Fuzzy logic theory is adopted to approximate unknown system function, and the controller was designed by combining sliding mode control with backstepping thought. Firstly, the longitudinal speed was controlled, then the yaw angle was made as input of path following error to design the calm function and the change rate of path parameters. The controller stability was proved by Lyapunov stable theory. Simulation and outfield tests were conducted and the results showed that the controller is of excellent adaptability and robustness in the presence of parameter uncertainties and external disturbances. It is also shown to be able to avoid the chattering of AUV actuator

3D Coordinated Path Following with Disturbance Rejection for Formations of Under-actuated Agents

In this paper coordinated path following for formations of under-actuated agents in three dimensional space is considered. The agents are controlled to follow a straight-line path whilst being affected by an unknown environmental disturbance. The problem is solved using a twofold approach. In particular, the agents are controlled to the desired path using a guidance law that rejects an unknown, but constant, disturbance. Simultaneously each agent utilises a decentralised nonlinear coordination law to achieve the desired formation. The closed-loop system of path-following and coordination dynamics is analysed using theory for feedback-interconnected systems. In particular, a technique from [1] is used that allows us to analyse a feedback-interconnected systems as a cascaded system. The origin of the closed-loop error dynamics is shown to be globally asymptotically stable. A case study with simulation results is presented to validate the control strategy.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Robust Controller Design for an Autonomous Underwater Vehicle

Worldwide there has been a surge of interest in Autonomous Underwater Vehicles (AUV). The ability to operate without human intervention is what makes this technology so appealing. On the other hand, the absence of the human narrows the AUV operation to its control system, computing, and sensing capabilities. Therefore, devising a robust control is mandatory to allow the feasibility of the AUV. Motivated by this fact, this thesis aims to present, discuss and evaluate two linear control solutions being proposed for an AUV developed by a consortium led by CEiiA. To allow the controller design, the dynamic model of this vehicle and respective considerations are firstly addressed. Since the purpose is to enable the vehicle’s operation, devising suitable guidance laws becomes essential. A simple waypoint following and station keeping algorithm, and a path following algorithms are presented. To devise the controllers, a linear version of the dynamic model is derived considering a single operational point. Then, through the decoupling of the linear system into three lightly interactive subsystems, four Proportional Integral Derivative controllers (PIDs) are devised for each Degree Of Freedom (DOF) of the vehicle. A Linear Quadratic Regulator (LQR) design, based on the decoupling of the linear model into longitudinal and lateral subsystems is also devised. To allocate the controller output throughout the actuators, a control allocation law is devised, which improves maneuverability of the vehicle. The results present a solid performance for both control methods, however, in this work, LQR proved to be slightly faster than PID.É visível, a nível mundial, um aumento considerável do interesse em Veículos Autónomos Subaquáticos (Autonomous Underwater Vehicles - AUV). O que torna esta tecnologia tão atraente é a capacidade de operar sem intervenção humana. Contudo, a ausência do ser humano restringe a operação do AUV ao seu sistema de controlo, computação e capacidades de detecção. Desta forma, conceber um controlo robusto é obrigatório para viabilizar o AUV. Motivado por este facto, esta tese tem como objetivo apresentar, discutir e avaliar duas soluções de controlo linear, a propor a um AUV desenvolvido por um consórcio liderado pelo CEiiA. Para que o projeto do controlador seja possível, o modelo dinâmico deste veículo e respectivas considerações são primeiramente abordados. Com a finalidade de possibilitar a operação do veículo, torna-se essencial a elaboração de leis de guidance adequadas. Para este efeito são apresentados algorítmos de Waypoint following e Station keeping, e de path following. Para a projeção dos controladores é derivada uma versão linear do modelo dinâmico, considerando um único ponto operacional. Através da separação do modelo linear em três subsistemas são criados quatro controladores Proporcional Integral Derivativo (PID) para cada grau de liberdade (Degree Of Freedom - DOF) do veículo. É também projetado um Regulador Linear Quadrático (LQR), baseado na separação do modelo linear em dois subsistemas, longitudinal e lateral. É ainda apresentada uma lei de alocação de controlo para distribuir o sinal de saída dos controladores pelos diferentes atuadores. Esta provou melhorar a manobrabilidade do veículo. Os resultados finais apresentam um desempenho sólido para ambos os métodos de controlo. No entanto, neste trabalho, o LQR provou ser mais rápido do que o PID

The predictive functional control and the management of constraints in GUANAY II autonomous underwater vehicle actuators

Autonomous underwater vehicle control has been a topic of research in the last decades. The challenges addressed vary depending on each research group's interests. In this paper, we focus on the predictive functional control (PFC), which is a control strategy that is easy to understand, install, tune, and optimize. PFC is being developed and applied in industrial applications, such as distillation, reactors, and furnaces. This paper presents the rst application of the PFC in autonomous underwater vehicles, as well as the simulation results of PFC, fuzzy, and gain scheduling controllers. Through simulations and navigation tests at sea, which successfully validate the performance of PFC strategy in motion control of autonomous underwater vehicles, PFC performance is compared with other control techniques such as fuzzy and gain scheduling control. The experimental tests presented here offer effective results concerning control objectives in high and intermediate levels of control. In high-level point, stabilization and path following scenarios are proven. In the intermediate levels, the results show that position and speed behaviors are improved using the PFC controller, which offers the smoothest behavior. The simulation depicting predictive functional control was the most effective regarding constraints management and control rate change in the Guanay II underwater vehicle actuator. The industry has not embraced the development of control theories for industrial systems because of the high investment in experts required to implement each technique successfully. However, this paper on the functional predictive control strategy evidences its easy implementation in several applications, making it a viable option for the industry given the short time needed to learn, implement, and operate, decreasing impact on the business and increasing immediacy.Peer ReviewedPostprint (author's final draft

Underwater Robots Part II: Existing Solutions and Open Issues

National audienceThis paper constitutes the second part of a general overview of underwater robotics. The first part is titled: Underwater Robots Part I: current systems and problem pose. The works referenced as (Name*, year) have been already cited on the first part of the paper, and the details of these references can be found in the section 7 of the paper titled Underwater Robots Part I: current systems and problem pose. The mathematical notation used in this paper is defined in section 4 of the paper Underwater Robots Part I: current systems and problem pose

무인잠수정의 조류 외란을 고려한 경로 추종 제어기 설계

학위논문 (석사)-- 서울대학교 대학원 공과대학 조선해양공학과, 2017. 8. 김용환.작동기수가 부족한 대표적인 운동체인 어뢰형 무인잠수정의 경로 추종 문제는 비선형성이 큰 시스템의 특성으로 인해 비선형 제어 분야에서 다양하게 연구되었다. 운항속도가 느리고 제어판의 크기가 상대적으로 작아 외란의 영향이 큰 구조적 특징으로 인해 조류와 같은 미지의 환경 외란과 모델링 불확실성은 어뢰형 무인잠수정의 경로 추종 문제에 있어서 극복해야하는 과제로 떠올랐다. 이를 해결하기 위해 복합 시선각 유도(Augmented LOS guidance) 기법 등 외란의 영향을 보상할 수 있는 유도 방식을 채택하거나 리아프노프 기법(Lyapunov method)을 활용한 제어 기법, 적응 제어 기법(Adaptive control) 등을 활용한 다양한 경로 추종 제어기가 제안되어왔다. 본 논문은 경로에 접하고 있는 경로 좌표계상에서의 경로 이탈 오차 값과 무인잠수정의 선체고정좌표계에서 측정되는 속도 성분들을 이용하여 목표 선수각(Desired angle)을 계산하는 새로운 형태의 비선형 유도 방식을 제안하였다. 시스템의 안정성을 위해 유도 법칙 계수가 이용되었으며, 리아프노프 안정성 이론을 이용하여 제안된 유도 방식의 경로 수렴성을 증명하였다. 제안된 유도 방식은 미끄러짐 속도(Side-slip velocity)가 존재하지 않는 경우 경로 추종에 가장 많이 활용되는 방식인 시선각 유도 법칙(LOS guidance)과 같은 형태를 띠게 된다. 2차원 직선 경로에 대한 경로 추종 시뮬레이션을 통해 시선각 유도(LOS guidance), 그리고 강화 시선각 유도 기법의 하나인 적분-시선각 유도(Integral-LOS guidance) 방식과 성능을 비교분석 하였다. 퍼센트 오버슈트(% Overshoot)와 경로 이탈 오차에 대한 비용 함수, 정상상태 오차(Steady-state error), 방향타 속도(Rudder rate)에 대한 비용 함수 등을 비교 분석한 결과, 제안된 유도 방식은 조류의 영향이 없는 환경에서는 다른 유도 방식과 비슷한 성능을 보였지만 조류가 있는 환경에서는 오버슈트와 경로 이탈 오차의 측면에서 성능이 뛰어남을 보였다. 모델링 불확실성과 미지의 외란을 고려하기 위해 제안된 유도 방식을 신경회로망 기반 적응 제어 기법에 적용하여 최종적인 경로 추종 제어기를 설계하였다. 작동기의 위치와 속도 포화도(saturation)에 따른 시스템의 비선형성에 신경회로망이 적응하여 성능이 저하되는 것을 방지하기 위해 PCH 기법을 사용하였다. 무인잠수정의 일반적인 구조적 특징에 따라 횡동요 운동이 생략된 5자유도 운동을 고려하였다. 또한 크기가 일정하고 비회전성인 조류 조류의 속력이 무인잠수정의 속력보다 작고 무인잠수정의 추력은 일정하다는 가정 하에 조류에 대한 외력을 조류에 대한 상대속도를 이용하여 단순화하였다. 조류에 대한 상대속도와 관련된 유체력 미계수와 조류 속도를 미지의 값으로 설정한 후, 운동방정식을 모델링이 된 항과 모델링되지 않은 항으로 구분하였다. 3차원 곡선 경로에 대한 경로 추종 시뮬레이션을 수행한 결과, 제안된 경로 추종 제어기의 적응 신호(Adaptive signal)가 운동방정식의 모델링 되지 않은 항에 수렴하는 것을 보였으며, 수평방향 경로 이탈 오차 0.1m 이내, 중력의 영향이 작용하는 수직방향의 경로 이탈 오차는 2m 이내로 충분히 우수한 경로 추종 성능을 보였다.제 1 장 서론 1 제 2 장 무인잠수정의 운동방정식 6 제 1 절 좌표계 설정 6 제 2 절 운동학(Kinematics) 9 제 3 절 운동방정식(Equations of Motion) 10 제 3 장 유도 법칙(Guidance Law) 14 제 1 절 유도-항법-제어 (GNC) 시스템 14 제 2 절 제어 목표(Control Object) 18 제 3 절 시선각 유도 법칙 19 제 4 절 적분-시선각 유도 법칙 21 제 5 절 비선형 시선각 유도 방식 22 제 1 항 유도 법칙 22 제 2 항 경로 수렴성 증명 23 제 3 항 비선형 시선각 유도 방식 특성 분석 26 제 4 장 제어기 설계 29 제 1 절 의사제어(Pseudo Control) 기법 29 제 2 절 신경회로망 기반 적응 제어 32 제 3 절 Pseudo Control Hedging (PCH) 기법 35 제 4 절 제어기 구성 37 제 5 장 시뮬레이션 39 제 1 절 시뮬레이션 조건 39 제 2 절 오픈루프 시뮬레이션 41 제 3 절 유도 방식에 따른 비교 45 제 4 절 3차원 곡선 경로 추종 49 결 론 54 참고문헌 56 Abstract 60Maste