Kinodynamic planning for a fixed-wing aircraft in dynamic, cluttered environments : a local planning method using implicitly-defined motion primitives

Cowley, Edwe Gerrit (2013-03)

Thesis (MScEng)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: In order to navigate dynamic, cluttered environments safely, fully autonomous Unmanned Aerial Vehicles (UAVs) are required to plan conflict-free trajectories between two states in position-time space efficiently and reliably. Kinodynamic planning for vehicles with non-holonomic dynamic constraints is an NP-hard problem which is usually addressed using sampling-based, probabilistically complete motion planning algorithms. These algorithms are often applied in conjunction with a finite set of simple geometric motion primitives which encapsulate the dynamic constraints of the vehicle. This ensures that composite trajectories generated by the planning algorithm adhere to the vehicle dynamics. For many vehicles, accurate tracking of position-based trajectories is a non-trivial problem which demands complicated control techniques with high energy requirements. In an effort to reduce control complexity and thus also energy consumption, a generic Local Planning Method (LPM), able to plan trajectories based on implicitly-defined motion primitives, is developed in this project. This allows the planning algorithm to construct trajectories which are based on simulated results of vehicle motion under the control of a rudimentary auto-pilot, as opposed to a more complicated position-tracking system. The LPM abstracts motion primitives in such a way that it may theoretically be made applicable to various vehicles and control systems through simple substitution of the motion primitive set. The LPM, which is based on a variation of the Levenberg-Marquardt Algorithm (LMA), is integrated into a well-known Probabilistic Roadmap (PRM) kinodynamic planning algorithm which is known to work well in dynamic and cluttered environments. The complete motion planning algorithm is tested thoroughly in various simulated environments, using a vehicle model and controllers which have been previously verified against a real UAV during practical flight tests.

AFRIKAANSE OPSOMMING: Ten einde dinamiese, voorwerpryke omgewings veilig te navigeer, word daar vereis dat volledig-outonome onbemande lugvoertuie konflikvrye trajekte tussen twee posisie-tydtoestande doeltreffend en betroubaar kan beplan. Kinodinamiese beplanning is ’n NPmoeilike probleem wat gewoonlik deur middel van probabilisties-volledige beplanningsalgoritmes aangespreek word . Hierdie algoritmes word dikwels in kombinasie met ’n eindige stel eenvoudige geometriese maneuvers, wat die dinamiese beperkings van die voertuig omvat, ingespan. Sodanig word daar verseker dat trajekte wat deur die beplaningsalgoritme saamgestel is aan die dinamiese beperkings van die voertuig voldoen. Vir baie voertuie, is die akkurate volging van posisie-gebaseerde trajekte ’n nie-triviale probleem wat die gebruik van ingewikkelde, energie-intensiewe beheertegnieke vereis. In ’n poging om beheer-kompleksiteit, en dus energie-verbruik, te verminder, word ’n generiese plaaslike-beplanner voorgestel. Hierdie algoritme stel die groter kinodinamiese beplanner in staat daartoe om trajekte saam te stel wat op empiriese waarnemings van voertuig-trajekte gebaseer is. ’n Eenvoudige beheerstelsel kan dus gebruik word, in teenstelling met die meer ingewikkelde padvolgingsbeheerders wat benodig word om eenvoudige geometriese trajekte akkuraat te volg. Die plaaslike-beplanner abstraeer maneuvers in so ’n mate dat dit teoreties op verskeie voertuie en beheerstelsels van toepassing gemaak kan word deur eenvoudig die maneuver-stel te vervang. Die plaaslike-beplanner, wat afgelei is van die Levenberg-Marquardt-Algoritme (LMA), word in ’n welbekende “Probabilistic Roadmap” (PRM) kinodinamiese-beplanningsalgoritme geïntegreer. Dit word algemeen aanvaar dat die PRM effektief werk in dinamiese, voorwerpryke omgewings. Die volledige beplanningsalgoritme word deeglik in verskeie, gesimuleerde omgewings getoets op ’n voertuig-model en -beheerders wat voorheen vir akkuraatheid teenoor ’n werklike voertuig gekontroleer is tydens praktiese vlugtoetse.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/80077
This item appears in the following collections: