Straight-line path following for asymmetric unmanned platform with disturbance estimation

The problem of straight-line path following for asymmetric unmanned platform exposed to unknown disturbances was addressed in this paper. The mathematical model of asymmetric unmanned platform was established and the inputs in sway and yaw directions were decoupled, which facilitated the establishment of control strategy of path following. The guidance law and the cross-track error were derived from the classical line-of-sight (LOS) guidance principle. And the equilibrium point of the cross-track error was proven to be uniformly semiglobally exponentially stable (USGES), which guaranteed the exponential convergence to zero. A new disturbance estimation law was developed by adding a linear item of the estimation error into the classical one, which improved the principle’s precision and sensitivity dramatically. The control strategy was developed based on the integrator backstepping technique and the new disturbance estimation law, which made the equilibrium system to be uniformly globally asymptotically stable (UGAS). Computer simulations were conducted to verify the effectiveness of the estimation and control laws during straight-line path following for asymmetric unmanned platform in the presence of unknown disturbances

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

Motion Control for Autonomous Navigation in Blue and Narrow Waters Using Switched Controllers

Autonomous ships represent one of the new frontiers of technological innovation in marine engineering, which demand the development of innovative control systems to guarantee efficient and safe navigation of vessels. A convenient control system should be able to command the several actuators installed on board in different conditions\u2014for instance, during oceanic navigation, harbor approach, narrow channels, and crowed areas. Such tasks are accomplished by different switching controllers for high and low speed motion, which have to be orchestrated to ensure an effective maneuvering. An approach to the design of hierarchies of controllers for maneuvering and navigation of ships equipped with a standard propulsion configuration in both blue and narrow water is proposed. Different levels of control, from global to local, are defined and integrated to steer the vessel in such a way to increase the maneuvering capability in various scenarios

Fuzzy-Based Optimal Adaptive Line-of-Sight Path Following for Underactuated Unmanned Surface Vehicle with Uncertainties and Time-Varying Disturbances

This paper investigates the path following control problem for an underactuated unmanned surface vehicle (USV) in the presence of dynamical uncertainties and time-varying external disturbances. Based on fuzzy optimization algorithm, an improved adaptive line-of-sight (ALOS) guidance law is proposed, which is suitable for straight-line and curve paths. On the basis of guidance information provided by LOS, a three-degree-of-freedom (DOF) dynamic model of an underactuated USV has been used to design a practical path following controller. The controller is designed by combining backstepping method, neural shunting model, neural network minimum parameter learning method, and Nussbaum function. Neural shunting model is used to solve the problem of “explosion of complexity,” which is an inherent illness of backstepping algorithm. Meanwhile, a simpler neural network minimum parameter learning method than multilayer neural network is employed to identify the uncertainties and time-varying external disturbances. In particular, Nussbaum function is introduced into the controller design to solve the problem of unknown control gain coefficient. And much effort is made to obtain the stability for the closed-loop control system, using the Lyapunov stability theory. Simulation experiments demonstrate the effectiveness and reliability of the improved LOS guidance algorithm and the path following controller

Finite-Time Observer Based Guidance and Control of Underactuated Surface Vehicles with Unknown Sideslip Angles and Disturbances

Suffering from complex sideslip angles, path following control of an under actuated surface vehicle (USV) becomes significantly challenging and remains unresolved. In this paper, a finite-time observer based guidance and control (FOGC) scheme for path following of an USV with time-varying and large sideslip angles and unknown external disturbances is proposed. The salient features of the proposed FOGC scheme are as follows: 1) time-varying large sideslip angle is exactly estimated by a finite-time sideslip observer, and thereby contributing to the sideslip-tangent line-of-sight guidance law which significantly enhances the robustness of the guidance system to unknown sideslip angles which are significantly large and time-varying; 2) a finite-time disturbance observer (FDO) is devised to exactly observe unknown external disturbances, and thereby implementing FDO-based surge and heading robust tracking controllers, which possess remarkable tracking accuracy and precise disturbance rejection, simultaneously; and 3) by virtue of cascade analysis and Lyapunov approach, global asymptotic stability of the integrated guidance-control system is rigorously ensured. Simulation studies and comparisons are conducted to demonstrate the effectiveness and superiority of the proposed FOGC scheme

A guiding vector field algorithm for path following control of nonholonomic mobile robots

In this paper we propose an algorithm for path following control of the nonholonomic mobile robot based on the idea of the guiding vector field (GVF). The desired path may be an arbitrary smooth curve in its implicit form, that is, a level set of a predefined smooth function. Using this function and the robot’s kinematic model, we design a GVF, whose integral curves converge to the trajectory. A nonlinear motion controller is then proposed which steers the robot along such an integral curve, bringing it to the desired path. We establish global convergence conditions for our algorithm and demonstrate its applicability and performance by experiments with wheeled robots

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

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

Reliable and Safe Motion Control of Unmanned Vehicles

Unmanned vehicles (UVs) are playing an increasingly significant role in modern daily life. In the past decades, numerous commercial, scientific, and military communities across the world are developing fully autonomous UVs for a variety of applications, such as environmental monitoring and surveillance, post-disaster search and rescue, border patrol, natural resources exploration, and experimental platforms for new technologies verification. The excessive opportunities and threats that come along with these diverse applications have created a niche demand for UVs to extend their capabilities to perform more sophisticated and hazardous missions with greater autonomy, lower costs of development and operation, improved personnel safety and security, extended operational range (reliability) and precision, as well as increased flexibility in sophisticated environments including so-called dirty, dull, harsh, and dangerous missions. In order to successfully and effectively execute missions and meet their corresponding performance criteria and overcome these ever-increasing challenges, greater autonomy together with more advanced reliable and safe motion control systems are required to offer the critical technologies for ensuring intelligent, safe, reliable, and efficient control of UVs in the presence of disturbances, actuator saturation, and even actuator faults, especially for practical applications. This thesis concentrates on the development of different reliable and safe motion control algorithms/strategies applicable to UVs, in particular, unmanned aerial vehicles (UAVs) and unmanned surface vehicles (USVs). A number of contributions pertaining to the fault detection and diagnosis (FDD), fault-tolerant control (FTC), disturbance estimation and compensation, and actuator saturation avoidance have been made in this thesis. In addition to the control problems, this thesis also presents several guidance-related contributions, including adaptive observer-based line-of-sight (LOS) guidance law, time-varying lookahead distance scheme, piecewise path switching criterion for guiding a single UV, as well as a proportional-integral (PI) type of leader-follower formation guidance strategy for a group of UVs