On-Orbit Manoeuvring Using Superquadric Potential Fields

On-orbit manoeuvring represents an essential process in many space missions such as orbital assembly, servicing and reconfiguration. A new methodology, based on the potential field method along with superquadric repulsive potentials, is discussed in this thesis. The methodology allows motion in a cluttered environment by combining translation and rotation in order to avoid collisions. This combination reduces the manoeuvring cost and duration, while allowing collision avoidance through combinations of rotation and translation. Different attractive potential fields are discussed: parabolic, conic, and a new hyperbolic potential. The superquadric model is used to represent the repulsive potential with several enhancements. These enhancements are: accuracy of separation distance estimation, modifying the model to be suitable for moving obstacles, and adding the effect of obstacle rotation through quaternions. Adding dynamic parameters such as object translational velocity and angular velocity to the potential field can lead to unbounded actuator control force. This problem is overcome in this thesis through combining parabolic and conic functions to form an attractive potential or through using a hyperbolic function. The global stability and convergence of the solution is guaranteed through the appropriate choice of the control laws based on Lyapunov's theorem. Several on-orbit manoeuvring problems are then conducted such as on-orbit assembly using impulsive and continuous strategies, structure disassembly and reconfiguration and free-flyer manoeuvring near a space station. Such examples demonstrate the accuracy and robustness of the method for on-orbit motion planning

Robust Path Following on Rivers Using Bootstrapped Reinforcement Learning

This paper develops a Deep Reinforcement Learning (DRL)-agent for navigation and control of autonomous surface vessels (ASV) on inland waterways. Spatial restrictions due to waterway geometry and the resulting challenges, such as high flow velocities or shallow banks, require controlled and precise movement of the ASV. A state-of-the-art bootstrapped Q-learning algorithm in combination with a versatile training environment generator leads to a robust and accurate rudder controller. To validate our results, we compare the path-following capabilities of the proposed approach to a vessel-specific PID controller on real-world river data from the lower- and middle Rhine, indicating that the DRL algorithm could effectively prove generalizability even in never-seen scenarios while simultaneously attaining high navigational accuracy

Modelling and control of a UAV-USV collaboration scheme for fluvial operations

This thesis focuses on a Model Based Design approach to the dynamic modelling and control design of a multi-robot solution based on a collab- oration scheme between a UAV and USV. The purpose of the system is to provide a suitable platform to autonomously perform limnology related surveys. The dynamic models of both platforms are derived from a Newton- Euler formalism and implemented through block oriented modelling us- ing the Simscape Multibody toolset within Simulink. The implementation of both the simulation architecture and the control architecture are de- scribed and explained. This control architecture is based on PID feedback loops that are used for achieving control of the UAV and USV dynamics. Finally, the built simulator is used to asses the performance and relia- bility of the designed controllers and the dynamic modelling approaches selectedIngeniería en Tecnologías Industriale

Navigation and Applicability of Hexa Rotor Drones in Greenhouse Environment

The paper discusses use-cases and a broad description of application possibilities of drones in greenhouses. Unmanned autonomous aerial vehicles (UAV), i.e. drones, are being used increasingly often for the direct or indirect collection of data. GPS navigation cannot be applied in an indoor work environment. One of the alternatives is to measure the distance from a fixed set of sensors with known positions. The paper presents a dynamic model for a hexa-rotor drone. In order to ensure reliable navigation a new navigation algorithm is presented based on the two-dimensional navigation algorithm of the robot motion control. It demonstrates the development of a threedimensional navigation algorithm for the hexa-rotor drone with the hypothesis that the elaborate three-dimensional model can navigate the drone in an indoor environment. To prove the hypothesis, the simulation is implemented in Scilab environment with information about the flight path deviation from the planned routes, which is also given in the work

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

Sailing with a ghost ship: Design guidelines for developing supervisory control interfaces for the semi-autonomous cargo vessel system

Rolls-Royce Marine is currently developing a semi-autonomous cargo vessel. The semi-autonomous cargo ship operation is a supervisory control task, in which the human operator is receiving information from a remote semi-autonomous vessel and instructing it through supervisory control interfaces. Thus, it is necessary to have supervisory control interfaces to carry the operation. But, the design guidelines for the interfaces are unclear, because of the lack of semi-autonomous cargo ships. The thesis presents design guidelines for developing supervisory control interfaces for the semi-autonomous cargo vessel. The research question answered in this thesis is: “How to design a supervisory control interface for remote semi-autonomous cargo vessel system to enable intuitive and precise instruction of the course plan?” The author answers the question through a research and design process that consists of the problem and solution spaces. The problem space suggests design requirements through a literature review and experts interviews. The literature review gives contextual and theoretical knowledge to design supervisory control interfaces. The expert interviews with video gamers and autonomous ship experts present potential user needs and design considerations. The findings from the problem space combine and formulate design requirements. The solution space ideates and prototypes a supervisory control interface prototype by applying the design requirements. The prototype has been evaluated in usability tests with sailors and autonomous ship expert. The findings from the usability tests are linked to the design requirements to evaluate how the designed solution fulfils design requirements. The thesis contributes to the design of semi-autonomous cargo vessel supervisory control interfaces by answering to the research question. In the conclusion part, the author answer to the research question by suggesting three design themes, which are synthetics of the design requirements and analysis. The design themes are: providing situation awareness, intuitive manipulation, and collaborative control. With these design themes designers will be able to develop supervisory control interfaces, which present intuitive and precise course planning capability to the operators. At the same time, the findings of the thesis will provide several directions for further research, such as researching an unmanned surface vehicle supervisory control interface

Toward on-line robot vibratory modes estimation

International audienceThis paper is concerned with preliminary results on robot vibratory modes on-line estimation. The dominating oscillatory mode of the robot arm is isolated by comparing the robot position given by the motors encoders and an external measure at the tool-tip of the robot arm. In this article the external measurement is provided by a laser tracker. The isolation of the oscillation permits to identify the vibratory mode, \textit{i.e.} the natural frequency and the damping ratio of the undesired phenomena. Here we propose a comparison between the algebraic method and the sliding modes for the parameter identification. This comparison is motivated by the fact that both methods provide finite time convergence. Experimental identifications are proposed on a 6 degrees of freedom (DOF) manipulator robot, Stäubli RX-170B