Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This thesis presents a complete state estimation framework for landing an unmanned
helicopter on a ship deck. In order to design and simulate an optimal state estimator,
realistic sensor models are required. Selected inertial, absolute and relative sensors
are modeled based on extensive data analysis. The short-listed relative sensors include
monocular vision, stereo vision and laser-based sensors.
A state estimation framework is developed to fuse available helicopter estimates, ship
estimates and relative measurements. The estimation structure is shown to be both
optimal, as it minimises variance on the estimates, and flexible, as it allows for varying
degrees of ship deck instrumentation. Deck instrumentation permitted ranges
from a fully instrumented deck, equipped with an inertial measurement unit and differential
GPS, to a completely uninstrumented ship deck. Optimal estimates of all
helicopter, relative and ship states necessary for the autonomous landing on the ship
deck are provided by the estimator. Active gyro bias estimation is incorporated into
the helicopter’s attitude estimator. In addition, the process and measurement noise
covariance matrices are derived from sensor noise analysis, rather than conventional
tuning methods.
A full performance analysis of the estimator is then conducted. The optimal relative
sensor combination is determined through Monte Carlo simulation. Results show
that the choice of sensors is primarily dependent on the desired hover height during
the ship motion prediction stage. For a low hover height, monocular vision is
sufficient. For greater altitudes, a combination of monocular vision and a scanning
laser beam greatly improves relative and ship state estimation. A communication
link between helicopter and ship is not required for landing, but is advised for added
accuracy. The estimator is implemented on a microprocessor running real-time Linux. The
successful performance of the system is demonstrated through hardware-in-the-loop
and actual flight testing. / AFRIKAANSE OPSOMMING: Hierdie tesis bied ’n volledige sensorfusie- en posisieskattingstruktuur om ’n onbemande
helikopter op ’n skeepsdek te laat land. Die ontwerp van ’n optimale posisieskatter
vereis die ontwikkeling van realistiese sensormodelle ten einde die skatter
akkuraat te simuleer. Die gekose inersie-, absolute en relatiewe sensors in hierdie
tesis is op grond van uitvoerige dataontleding getipeer, wat eenoogvisie-, stereovisieen
lasergegronde sensors ingesluit het.
’n Innoverende raamwerk vir die skatting van relatiewe en skeepsposisie is ontwikkel
om die beskikbare helikopterskattings, skeepskattings en relatiewe metings te kombineer.
Die skattingstruktuur blyk optimaal te wees in die beperking van skattingsvariansie,
en is terselfdertyd buigsaam aangesien dit vir wisselende mates van skeepsdekinstrumentasie
voorsiening maak. Die toegelate vlakke van dekinstrumentasie
wissel van ’n volledig geïnstrumenteerde dek wat met ’n inersiemetingseenheid en ’n
differensiële globale posisioneringstelsel (GPS) toegerus is, tot ’n algeheel ongeïnstrumenteerde
dek. Die skatter voorsien optimale skattings van alle vereiste helikopter-,
relatiewe en skeepsposisies vir die doeleinde van outonome landing op die skeepsdek.
Aktiewe giro-sydige skatting is by die posisieskatter van die helikopter ingesluit. Die
proses- en metingsmatrikse vir geruiskovariansie in die helikopterskatter is met behulp
van ’n ontleding van sensorgeruis, eerder as gebruiklike instemmingsmetodes,
afgelei. ’n Volledige werkingsontleding is daarna op die skatter uitgevoer. Die optimale relatiewe
sensorkombinasie vir landing op ’n skeepsdek is met Monte Carlo-simulasie
bepaal. Die resultate toon dat die keuse van sensors hoofsaaklik van die gewenste
sweefhanghoogte gedurende die voorspellingstadium van skeepsbeweging afhang.
Vir ’n lae sweefhanghoogte is eenoogvisie-sensors voldoende. Vir hoër hoogtes het
’n kombinasie van eenoogvisie-sensors en ’n aftaslaserbundel ’n groot verbetering in
relatiewe en skeepsposisieskatting teweeggebring. ’n Kommunikasieskakel tussen helikopter
en skip is nie ’n vereiste vir landing nie, maar word wel aanbeveel vir ekstra
akkuraatheid.
Die skatter is op ’n mikroverwerker met intydse Linux in werking gestel. Die suksesvolle werking van die stelsel is deur middel van hardeware-geïntegreerde simulasie
en werklike vlugtoetse aangetoon.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95894 |
| Date | 12 1900 |
| Creators | Irwin, Shaun George |
| Contributors | Jones, Thomas, Stellenbosch University. Faculty of Engineering. Department of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xx, 108 p. : ill. |
| Rights | Stellenbosch University |
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