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Precise Motion Control of a Space Robot for In-Orbit Close Proximity Manoeuvres

Seddaoui, Asma (2020) Precise Motion Control of a Space Robot for In-Orbit Close Proximity Manoeuvres Doctoral thesis, University of Surrey.

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Space robotic solutions are gaining importance for undertaking in-orbit operations such as maintenance and repair, assembly of large structures, manufacturing and debris removal. The modelling and control of space robots is highly challenging due to (i) the inherent nonlinearities in the system, (ii) the dynamic coupling between the arm and the spacecraft base and (iii) the complex structure of two coupled systems i.e. a six Degree of Freedom (DoF) spacecraft base and an n DoF robotic arm. In addition to the aforementioned challenges, performing a precise motion of a space robot in the presence of environmental disturbances whilst considering the changes in the mass of the spacecraft base due to fuel consumption, is very intricate. Taking into account the above-mentioned challenges, this research is aimed at developing new control methodologies for precise manoeuvring of a space robot to safely capture a target in-orbit. Performing such fine motion control requires high precision manoeuvres by a space robot capable of tracking the grasping point on the target without a priori knowledge of the path to follow, whilst avoiding collisions and singularities. This research introduces a new mode of operation for space robots, defined as the controlled-floating mode. It allows the base of the space robot to move, in a controlled manner, simultaneously and in coordination with the arm to help reach the grasping point through following optimal trajectories for both the arm and its base. Unlike the classical free-flying and free-floating modes of operation, the controlled- floating mode offers extra DoFs, redundancy and unlimited workspace to the robotic arm of the space robot. The space robot, when operated in this mode, is hereafter referred to as the Controlled Floating Space Robot (CFSR). To control the motion of the CFSR, a new adaptive combined nonlinear Hinf controller was designed; it takes into account both external disturbances and internal parametric uncertainties due to the changes in the mass of the spacecraft base. This controller guarantees robustness when compared to the traditional linear controllers, such as the Proportional-Integral-Derivative controller and the Linear Quadratic Regulator. Approaching the target when the grasping point is out of its reach or when the motion of the arm is restricted by singular configurations and obstacles, is a difficult task using the arm's n DoFs only. Hence, in this research, an optimal trajectory generator for both the arm and its base, using a Genetic Algorithm, was developed. This novel algorithm ensures that the selected path is free of singularities and obstacles whilst using minimal energy. This algorithm requires only the Cartesian location of the grasping point, to generate a path for the space robot without a priori knowledge of the desired path.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors :
Seddaoui, Asmaa.seddaoui@gmail.com0000-0002-5971-3254
Date : 2020
Funders : UK space Agency’s Centre for Earth Observation Instrumentation, Surrey Satellite Technology Limited, Algerian Space Agency
DOI : 10.15126/thesis.00854089
Contributors :
ContributionNameEmailORCID, Chakravarthini
Depositing User : Asma Seddaoui
Date Deposited : 19 May 2020 12:29
Last Modified : 20 May 2020 07:31

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