A new guidance law for trajectory tracking of an underactuated unmanned surface vehicle with parameter perturbations

Publisher’s embargo period: Embargo set on 01.03.2019 by SR (TIS)

Experimental Validation Of An Integrated Guidance And Control System For Marine Surface Vessels

Autonomous operation of marine surface vessels is vital for minimizing human errors and providing efficient operations of ships under varying sea states and environmental conditions which is complicated by the highly nonlinear dynamics of marine surface vessels. To deal with modelling imprecision and unpredictable disturbances, the sliding mode methodology has been employed to devise a heading and a surge displacement controller. The implementation of such a controller necessitates the availability of all state variables of the vessel. However, the measured signals in the current study are limited to the global X and Y positioning coordinates of the boat that are generated by a GPS system. Thus, a nonlinear observer, based on the sliding mode methodology, has been implemented to yield accurate estimates of the state variables in the presence of both structured and unstructured uncertainties. Successful autonomous operation of a marine surface vessel requires a holistic approach encompassing a navigation system, robust nonlinear controllers and observers. Since the overwhelming majority of the experimental work on autonomous marine surface vessels was not conducted in truly uncontrolled real-world environments. The first goal of this work was to experimentally validate a fully-integrated LOS guidance system with a sliding mode controller and observer using a 16’ Tracker Pro Guide V-16 aluminium boat with a 60 hp. Mercury outboard motor operating in the uncontrolled open-water environment of Lake St. Clair, Michigan. The fully integrated guidance and controller-observer system was tested in a model-less configuration, whereby all information provided from the vessel’s nominal model have been ignored. The experimental data serves to demonstrate the robustness and good tracking characteristics of the fully-integrated guidance and controller/observer system by overcoming the large errors induced at the beginning of each segment and converging the boat to the desired trajectory in spite of the presence of environmental disturbances. The second focus of this work was to combine a collision avoidance method with the guidance system that accounted for “International Regulations for Prevention of Collisions at Sea” abbreviated as COLREGS. This new system then needed to be added into the existing architecture. The velocity obstacles method was selected as the base to build upon and additional restrictions were incorporated to account for these additional rules. This completed system was then validated with a software in the loop simulation

Adaptive depth control algorithms for an autonomous underwater vehicle

Research on Autonomous Underwater Vehicle (AUV) has been increasing in the recent years. These robotics have the ability to revolutionize access to the oceans to address critical problems facing the marine community such as underwater search and mapping, water column observations climate change assessment, marine habitat monitoring, and underwater mine detection. In this thesis an adaptive nonlinear controller for steering the dynamic model of an autonomous underwater vehicle (AUV) onto a predefined path at a constant forward speed along a desired path is being presented. In this we have used two different controllers for dive plane control of an AUV. In one case, the diving dynamics of an AUV is derived under the assumptions that the pitch angle of AUV is small in the diving plane motion of the vehicle. Autonomous Underwater Vehicles’ dynamics are highly nonlinear and the hydrodynamic coefficients of the vehicles are difficult to determine due to the variations of the hydrodynamic coefficients with different operating conditions of the environment. These kinds of difficulties cause modeling inaccuracies of AUV’s dynamics. So in order to achieve robustness against parameter uncertainty, system identification technique based on Model Reference Adaptive Controller (MRAC) using MIT rule and Fuzzy Logic Controller (FLC) is employed for modeling the AUV dynamics. In this thesis MRAC technique is being proposed for the dynamics control and for the kinematics control of an Autonomous Underwater Vehicle we have used the FLC .Simulation results are being shown which shows effective dive-plane control in spite of the dynamic uncertainties. However in the second case we have proposed a dive plane controller based on Lyapunov theory and Backstepping techniques, where the dynamics of the AUV is being considered without keeping any restricting assumptions on AUV’s pitch angle

Task-space dynamic control of underwater robots

This thesis is concerned with the control aspects for underwater tasks performed by marine robots. The mathematical models of an underwater vehicle and an underwater vehicle with an onboard manipulator are discussed together with their associated properties. The task-space regulation problem for an underwater vehicle is addressed where the desired target is commonly specified as a point. A new control technique is proposed where the multiple targets are defined as sub-regions. A fuzzy technique is used to handle these multiple sub-region criteria effectively. Due to the unknown gravitational and buoyancy forces, an adaptive term is adopted in the proposed controller. An extension to a region boundary-based control law is then proposed for an underwater vehicle to illustrate the flexibility of the region reaching concept. In this novel controller, a desired target is defined as a boundary instead of a point or region. For a mapping of the uncertain restoring forces, a least-squares estimation algorithm and the inverse Jacobian matrix are utilised in the adaptive control law. To realise a new tracking control concept for a kinematically redundant robot, subregion tracking control schemes with a sub-tasks objective are developed for a UVMS. In this concept, the desired objective is specified as a moving sub-region instead of a trajectory. In addition, due to the system being kinematically redundant, the controller also enables the use of self-motion of the system to perform sub-tasks (drag minimisation, obstacle avoidance, manipulability and avoidance of mechanical joint limits)

Dynamics and Control of a Multi-Rotor Aircraft

Despite the fact that aerodynamic loads (forces and moments) induced by airflow relative to a quadrotor vertical take-off and landing aircraft consist of both deterministic and stochastic components, all existing works on controlling the aircraft either ignore these loads or treat them as deterministic. This simplification deteriorates the control performance in a practical implementation. This thesis presents a constructive design of controllers for a quadrotor aircraft to track a reference path in three-dimensional space under both deterministic and stochastic aerodynamic loads

Control design using energy-shaping methods

The aim of this research project was to investigate the benefits and shortfalls of Energy- Shaping controllers and use them to gain insight into industry standard control methods. Energy is a fundamental quantity in nature and is conserved due to the first law of thermodynamics. Actuators, necessarily, add energy into the system or remove energy from the system. Sensors remove (in some cases, negligible amounts of) energy from the system in order to measure some variable of interest. All control algorithms employing feedback, must measure at least one physical variable of the system to be controlled. Furthermore, all control algorithms must have at least one actuator in order to control the system. Hence, by proxy, all control algorithms affect the energy of the system. Two key ideas in energy shaping are: Energy Balancing and Power Shaping. Other control algorithms, ultimately, can be classed under these two ideas. Three constructive energy shaping algorithms were investigated, these were: Controller Interpolation via a common Lyapunov function, Energy- Shaping Robot control and Interconnection and Damping Assignment Passivity Based Control (IDAPBC). In this dissertation, a modelling paradigm has been proposed which is a multi-dimensional extension of The Energy Method. It is also shown that dissipation acts as a constant disturbance in the power of the system. A non-linear PI-like controller has been proposed to compensate for it. A clear link between the phase portrait and the system’s energy is shown. By shaping the system energy, the phase portrait is altered and by shaping the phase portrait, the time domain performance is altered. In this dissertation, the various techniques used to shape a system’s energy and power are all applied to the same non-linear control problem i.e. the simple pendulum. With hindsight, popular existing control strategies are reinterpreted via energy and power shaping. A notable example is that PID is shown to affect the potential and dissipation functions of the closed loop system. A pattern that emerged during the research was that: in order to fully control the system, it appears that the controller must be at least as computationally complicated as the plant. This is dubbed, the Controller Complexity Principle. A formal proof of it is a recommended research direction. The main conclusion of this work is that energy and power are concepts of tremendous value in control engineering. In this dissertation, energy and power are used to tie seemingly disparate work in control together. It is this re-interpretation of existing techniques in terms of energy and power which demonstrates the value of physical reasoning in control

Sliding Mode Control

The main objective of this monograph is to present a broad range of well worked out, recent application studies as well as theoretical contributions in the field of sliding mode control system analysis and design. The contributions presented here include new theoretical developments as well as successful applications of variable structure controllers primarily in the field of power electronics, electric drives and motion steering systems. They enrich the current state of the art, and motivate and encourage new ideas and solutions in the sliding mode control area