Design, Control, and Autonomous Navigation of Tilt–Rotor Unmanned Aerial Vehicles

262 Pages·2015·33.21 MB·English

by  Christos Papachristos

UNIVERSITY OF PATRAS
Design, Control, and Autonomous
Navigation of Tilt–Rotor
Unmanned Aerial Vehicles
by
Christos Papachristos
A Dissertation submitted for the
degree of Doctor of Philosophy
in the
Department of Electrical & Computer Engineering
PhD Dissertation Nr: 330
September 21, 2015
ii
PANEPISTHMIO PATRWN
&
Tm ma Hlektrolìgwn Mhqanik¸n Teqnologa
Upologist¸n
Qr sto
Papaqr sto
© 2015 –
Me thn epifÔlaxh pantì
dikai¸mato

UNIVERSITY OF PATRAS
Abstract
Department of Electrical & Computer Engineering
ANeMoS Research Group
Doctor of Philosophy Dissertation
by Christos Papachristos
This Dissertation addresses the design and development of small-scale Unmanned
Aerial Vehicles of the TiltRotor class, alongside their autonomous navigation re-
quirements, including thefully-onboardstateestimation, high-efficiency flight con-
trol, and advanced environment perception.
Starting with an educated Computer Assisted Design-based methodology, a me-
chanically robust, customizable, and repeatable vehicle build is achieved, relying
on high-quality Commercially Available Off-The Shelf equipment –sensors, actua-
tors, structural components–, optionally aided by Rapid Prototyping technology.
A high-fidelity modeling process is conducted, incorporating the rigid-body dy-
namics, aerodynamics, and the actuation subsystem dynamics, exploiting fist-
principle approaches, Frequency Domain System Identification, as well as com-
putational tools. Considering the most significant phenomena captured in this
process, a more simplified PieceWise Affine system model representation is devel-
oped for control purposes –which however incorporates complexities such as flight
(state) envelope-associated aerodynamics, the differentiated effects of the direct
thrust-vectoring (rotor-tilting) and the underactuated (body-pitching) actuation
authorities, as well as their interferences through rigid-body coupling–.
Despite the switching system dynamics, and –as thoroughly elaborated– their
reliance on constrained manipulated variables, to maintain a meaningful control-
orientedrepresentation, thereal-timeoptimalflightcontroloftheTiltRotorvehicle
is achieved relying on a Receding Horizon methodology, and more specifically an
explicit Model Predictive Control framework. This synthesis guarantees global
stability of the switching dynamics, observance of state and control input con-
straints, response optimality, as well as efficient execution on low computational
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power modules due to its explicit representation. Accompanied by a proper Low-
and-Mid-Level Control synthesis, this scheme provides exceptional flight handling
qualities to the aerial vehicle, particularly in the areas of aggressive maneuvering
and high-accuracy trajectory tracking.
Moreover, the utility of TiltRotor vehicles in the field of aerial robotic forceful
physical interaction is researched. Exploiting the previously noted properties of
the PieceWise Affine systems Model Predictive Control strategy, the guaranteed-
stability Free-Flight to Physical-Interaction switching of the system is achieved,
effectively bringing the aerial vehicle into safe, controlled physical contact with
the surface of structures in the environment.
Moreimportantly,employingrotor-tiltingactuation–collectivelyanddifferentially–
significant forces and moments can be applied onto the environment, while via the
standard underactuated authority the vehicle maintains a stable hovering-attitude
pose, where the system’s disturbance rejection properties are maximized. Overall,
the complete control framework enables coming into physical contact with envi-
ronment structures, and manipulating the enacted forces and moments. Exploit-
ing such capabilities the TiltRotor is used to achieve the execution of physically-
demanding work-tasks (surface-grinding) and the manipulation of realistically-
sized objects (of twice its own mass) via pushing.
Additionally, the fully-onboard state estimation problem is tackled by imple-
menting data fusion of measurements derived from inertial sensors and custom-
developed computer vision algorithms which employ Homography and Optical
Flow calculation. With a proper sensorial setup, high-rate and robust ego-motion
estimation is achieved, enabling the controlled aggressive maneuverability with-
out reliance on external equipment, such as motion capture systems or Global
Positioning System coverage.
Finally, a hardware/software framework is developed which adds advanced au-
tonomousperceptionandnavigationcapabilitiestosmall-scaleunmannedvehicles,
employing stereo vision and integrating state-of-the art solutions for incremen-
tal environment building, dense reconstruction and mapping, and point-to-point
collision-free navigation. Within this framework, algorithms which enable the de-
tection, segmentation, (re-)localization, and mobile tracking –and avoidance– of a
dynamicsubject withintheaerialvehicle’s operatingspacearedeveloped, substan-
tially increasing the operational potential of autonomous aircraft within dynamic
environments and/or dynamically evolving missions.
Acknowledgements
With every person, every PhD Candidate, it’s a different story; however we allare-
or-have been part of this year-long cycle of trying & failing to eventually succeed,
investing huge amounts of effort only to experience countless disappointments
before leading ourselves to the exceptional joy of accomplishment, and with each
breakthrough serving only as a realization of the long & labyrinthian path laying
ahead. From this rite of passage, we all come out changed, better-equipped and
more determined to face the personal choices and scientific challenges which will
allow us to play our smaller-or-larger roles in the history of humankind’s progress.
It is however with great pleasure to traverse even the weariest of roads with others,
supporters, advisors, companions, friends, and family –if not nearly impossible
without them–. This is hence the time to address and grant a “thank you” where
it is due.
It has been a truly remarkable experience working alongside my PhD supervi-
sor –but more significantly my advisor–, Professor Anthony Tzes. Since day one,
there has never been a time when I did not feel encouraged when discussing over
our research plans; his support for attempting even those “too-far-outside-the-
box” ideas, has consistently been with me along my PhD path. And when the
time for putting-those-feet-back-on-the-ground came, especially during the final
preparation process, he was there to help put everything into order. I will forever
remember Professor Peter Groumpos, whose aptitude in connecting science and
the broader academia with a perspective on worldwide politics and the economy
hasalsogivenmecountlesshoursoftalks, asourceofinspirationabouttheimpacts
of scientific research on everyday life. Moreover it is important for me to mention
Professor Kimon Valavanis, whose insightful contribution –even from continents
afar– in robustifying the essence and content of this Dissertation is reflected in nu-
merous points and passages throughout the full extent of this work. Additionally,
I would like to thank the Professors of the “Seven-member Committee”, Vagge-
lis Dermatas, Nikos Kousoulas, Kostas Kyriakopoulos, and Stamatis Manesis for
their well-posed and productive comments that helped revise this Dissertation to
its current corroborated form.
As a member of the ANeMoS group, it was an honor being beside and among
friends and colleagues, partaking in everyday Lab research work and academic
duties, sharing concerns and joys, helping and being aided when circumstances
ix
called for it. Younger and older alike, everyone had a role to play throughout these
years –and hence– became part of the complex process that produced this work:
John Arvanitakis,Nikos Evaggeliou,Rania Tsilomitrou,Eleni Kelasidi,George An-
drikopoulos, Dimos Tzoumanikas, Yannis Koveos, Yiannis Stergiopoulos, Stathis
Kountouras, Kostis Giannousakis, and last but not least, Michalis Thanou whom
we will always dearly miss. Moreover, it is important to mention those collabo-
rations that “stuck” in time, Associate Professor George Nikolakopoulos and As-
sistant Professor Kostas Alexis whose endeavours in high-caliber research gave me
the opportunity to partake in the formulation process –and be inspired by– the
next generation of aerial robotics research objectives.
A special “thank you” goes out to Kostas Alexis, whom I came to know as a PhD
CandidateinthissameLab4yearsago,IhavecollaboratedwithasanETH-Zu¨rich
Post-Doc researcher during the time since, and is now an Assistant Professor at
the University of Nevada, Reno. You may be an endless source of professional
motivation, but to the eyes of an “individual” you will always be the friend and
companion, “Kostalexis”.
It comes finally with great personal joy to dedicate this Dissertation to my family
Grigoris and Rania, and Dimitris my younger brother. No matter the circum-
stances, no matter the size of the obstacle, they have always stood by my side
throughout all these years, supporting me in every sense and manner. Through
practice, they have taught me the most invaluable lesson: that the pain of remain-
ing unyielding in support of another person’s endeavours will always fade under
the shade of seeing that person grow to reach their goals.